International police agency Interpol said on Thursday it was reviewing a request by Ukrainian authorities for it to issue a so-called "red notice" for the arrest of Viktor Yanukovich, who was ousted as its president.
"A request by Ukrainian authorities for an Interpol Red Notice, or international wanted persons alert, for the arrest of Viktor Yanukovich on charges including abuse of power and murder has been received," the France-based agency said in a statement.
This comes after Ukraine's acting president said a referendum planned by the pro-Moscow parliament in Crimea on joining Russia was illegitimate, and declared it a farce and crime organised by the Russian military.
In a short televised address, Oleksander Turchinov said the Ukrainian parliament would start procedures to dismiss the Crimean assembly and block the referendum.
"It is not a referendum, it is a farce, a fake and a crime against the state which is organised by the Russian Federation's military," he said, standing in front of the blue and yellow national flag.
For his part, Ukraine's Prime Minister Arseny Yatseniuk told a news conference that Ukraine's armed forces will act if Russian military intervention escalates any further in to Ukraine's territory.
"In case of further escalation and military intervention into the Ukrainian territory by foreign forces, the Ukrainian government and Ukrainian military will act in accordance with the constitution and laws," Yatseniuk said in Brussels.
"We are ready to protect our country," he said.
Ukrainian forces have so far not responded to the Russian takeover of the Crimean peninsula. But this could change if the Russian intervention escalated, he said.
Yatseniuk, who came to Brussels to discuss the crisis with the leaders of the 28 countries of the European Union, said the talks with EU leaders were only about political and peaceful means of resolving the conflict.
Ukraine's PM Yatseniuk also said that a decree making Crimea part of Russia was an illegitimate move and Crimea was and will remain an integral part of the country.
"This is an illegitimate decision and this so-called referendum has no legal grounds at all. That's the reason why we urge the Russian government not to support those who support separatism in the Ukraine," Yatseniuk told a news conference in Brussels following talks with EU leaders.
He also urged Russia to withdraw its military from Crimea and said the current crisis must be resolved only through peaceful means.
The crisis in Ukraine escalated on Thursday after the parliament in Crimea, which has effectively been seized by Russian forces, voted to join Russia.
Also on Thursday, the Russian-controlled region's deputy prime minister said the decree making Crimea part of Russia is already in force and Ukrainian troops still on its territory will be treated as occupiers and forced to surrender or leave.
"The only lawful armed force on the territory of the Crimea is the Russian armed forces," Rustam Temirgaliev said.
He also said that a referendum on the region's status would take place on March 16, RIA news agency reported.
EU:
European Union leaders agreed to suspend visa and investment talks with Russia on Thursday in reaction to its seizure of Crimea, and said they would freeze Russian assets and withdraw from a G8 summit if Russia does not reverse course.
After six hours of talks to discuss how to respond to Russia's manoeuvres against Ukraine, EU leaders took more far-reaching action than expected, spurred in part by a decision in the Crimean parliament to secede from Ukraine and join Russia.
"We have today decided to take actions ... notably to suspend bilateral talks with the Russian Federation on visa matters as well as talks with the Russian Federation on the new agreement" on investment and research cooperation, EU leaders said.
They also backed a decision by Britain, France, Germany and Italy - the European members of the G8 - to suspend preparations for the G8 summit in Sochi in June, with the possibility of calling off participation altogether if Russia does not engage in efforts to resolve the military stand-off.
"The solution to the crisis should be found through negotiations between the governments of Ukraine and the Russian Federation, including through potential multilateral mechanisms," European Council President Herman Van Rompuy said, reading from a communique agreed by all 28 EU leaders.
"Such negotiations need to start within the next few days and produce results within a limited time frame."
Diplomats said the EU's aim was to set out a three-step process, with sanctions pressure steadily increasing if Russia does not respond and start to engage in mediation.
Beyond the suspension of visa and investment talks, and the potential withdrawal from the G8 meeting, the EU will consider imposing travel restrictions on Russian officials, an arms embargo and asset freezes.
"Any further steps by the Russian Federation to destabilise the situation in Ukraine would lead to severe and far-reaching consequences for relations between the European Union and its member states on the one hand, and the Russian Federation on the other, which will include a broad range of economic areas," Van Rompuy said.
Earlier, U.S. President Barack Obama imposed travel bans on a number of Russian officials, although the White House said Russian President Vladimir Putin was not on the initial list.
As well, the European Union has frozen the assets of ousted Ukrainian president Viktor Yanukovich and 17 other officials, including former prime minister Mykola Azarov, suspected of violations of human rights and misuse of state funds.
The EU regulation, published in the Official Journal of the European Union on Thursday, applies within the territory of the EU, including its airspace.
The list also includes the former head of Ukraine's security service, a former prosecutor general, a former interior minister and a former justice minister.
CIS:
A meeting of former Soviet states grouped in the Commonwealth of Independent States (CIS) will take place on April 4, but a meeting of diplomats from Russia and Ukraine could take place before then, RIA news agency reported.
RIA quoted Deputy Foreign Minister Vasily Nebenzya as saying: "On April 4 there will be regular meeting of the CIS Council of Foreign Ministers in Moscow, and maybe there will be meetings before that time, including with the Ukrainians."
OSCE
A mission of observers from the Organization for Security and Cooperation in Europe (OSCE) has been stopped from entering Ukraine's Crimean Peninsula by unidentified men in military fatigues, Poland's defense minister said.
"The mission has been detained, they cannot go further. They landed in Odessa and they were traveling by car from Odessa towards the Crimean Peninsula, but they were detained by unidentified men in fatigues," the defense minister, Tomasz Siemoniak, told reporters.
He said it was possible the observers would be allowed to head back the way they came, but they could not go forward into Crimea. Two Polish military officers are among the OSCE mission.
NATO:
NATO urged Russia to call back to bases its forces on the Ukrainian Crimea peninsula, saying it stood by Ukraine's territorial integrity in the face of the greatest threat to European security since the end of the Cold War.
"Ukraine is a valued and long-standing partner for NATO. In these difficult moments NATO stands by Ukraine, NATO stands by Ukraine's sovereignty, integrity and by the fundamental principles of international law," NATO Secretary General Anders Fogh Rasmussen said.
The crisis in Ukraine escalated on Thursday after the parliament in Crimea, which has effectively been seized by Russian forces, voted to join Russia.
"This crisis is not just about Ukraine, this crisis has serious implications for the security and stability of the Euro-Atlantic area as a whole. We clearly face the gravest threat to European security since the end of the Cold War," Rasmussen said.
"Above all we call on Russia to step up its international commitments and halt the military escalation in Crimea. We call on Russia to withdraw its forces to their bases and to refrain from any interference elsewhere in Ukraine," he said.
Poland:
The U.S. military will send 12 F-16 fighter jets and 300 service personnel to Poland next week for a training exercise whose scope was expanded in response to the crisis in neighbouring Ukraine, Poland's defence minister said on Thursday.
Tomasz Siemoniak said the training exercise, centred on the Lask air force base in central Poland, was originally to have been smaller and involved only transport aircraft. He said Poland requested it be beefed up after Russia's intervention in Ukraine's Crimea Peninsula.
Standing at a news briefing alongside the minister, U.S. ambassador to Poland Stephen Mull said: "When we face such a dramatic challenge for our security, we need to reassure our allies that our security guarantees are valid."
Earlier, the Polish Prime Minister Donald Tusk said that the European Union should urgently sign an association agreement with Ukraine.
"I propose the urgent signing of the association agreement. There is a chance. But the opposition will be strong," Tusk said in a post on Twitter.
Also on Thursday, Russian President Vladimir Putin discussed Ukraine, including the Crimean parliament's appeal to let the region join Russia, at a meeting of his Security Council on Thursday, RIA news agency quoted his spokesman as saying.
This as Russia's Foreign Ministry said EU moves to consider freezing talks on a visa-free regime with Russia were "politicised, unconstructive and ungrounded" and expressed hope it would not happen.
"We still hope that at the end of the day our partners will not go for such a move," the ministry's spokesman Alexander Lukashevich said in a statement.
Earlier in the day, Russian Foreign Minister Sergei Lavrov said attempts by "our partners" to take action over the Ukraine crisis via democracy watchdog OSCE and the NATO military alliance were not helping cooperation and dialogue.
The European Union is ready to put in place further sanctions against Russia if it de-stabilises Ukraine further, French President Francois Hollande said after a European crisis meeting on the stand-off on Wednesday.
"If Russia ... took measures which de-stabilised Ukraine, called into question its territorial integrity, there would be new measures concerning ties between the EU and Russia in a number of economic sectors," Hollande told a news briefing.
EU officials said earlier that the 28-member bloc had decided to suspend bilateral talks on visas with Russia and suspend preparations for a G8 meeting. Other measures including freezes on individuals' assets and travel bans were also possible, they said.
British Prime Minister David Cameron warned the Kremlin on Thursday that Russians could face asset freezes and travel bans unless there was progress in direct talks with the new Ukrainian government.
Cameron, speaking after a meeting of European Union heads of state in Brussels, said the EU had agreed to suspend negotiations on easing visa rules for Russians in response to President Vladimir Putin's intervention in Ukraine.
"What has happened with respect to the Crimea is unacceptable and there can be no business as usual with Russia," Cameron told reporters.
He said the EU could move "relatively quickly" to asset freezes and travel bans unless Russia made progress in talks with Ukraine.
"If the talks don't get under way and if the talks don't make rapid progress, then we move to the second stage which is asset freezes and travel bans and that again could happen relatively quickly if progress isn't made," he said.
He said that if Russia went further into Ukraine or attempted to further destabilise its neighbour, there would be far-reaching economic consequences for Russia.
"My position is that this referendum is unconstitutional," the minister, Pavlo Sheremeta, told reporters in the Ukrainian capital Kiev, reiterating the government's stance following a decision by Crimea's new leaders to bring the referendum forward by two weeks to March 16.
The deputy speaker of the regional parliament in Crimea said the referendum would ask voters whether they want to be part of the Russian Federation.