One person was killed and several were treated for injuries in hospital on Thursday when hundreds of Ukrainian demonstrators clashed in the eastern city of Donetsk, the local health authority said.
Several hundred people chanting slogans praising Russian President Vladimir Putin clashed with a similar-sized crowd condemning Moscow's takeover of Crimea on a central square in the mainly Russian-speaking industrial city.
It was unclear how the dead person was killed. Protesters broke through a police cordon keeping the two sides apart. It was the first death reported in recent Ukrainian violence outside of the capital, Kiev.
This comes as Ukraine's acting president said that Russian forces were concentrated on the border "ready to invade" but he believed international efforts could end Moscow's "aggression" and avert the risk of war.
A statement on the presidential website said Oleksander Turchinov told a local television channel that, when Russian forces took over the southern region of Crimea last week, other units were concentrated on Ukraine's eastern border "ready for an invasion of the territory of Ukraine at any moment".
"We are doing all we can to avoid war, whether in Crimea or in any other region of Ukraine," he said, adding that Ukraine's own armed forces were in a state of full combat readiness.
However, he said: "All of civilized humanity supports our country. All the leading countries of the world are on the side of Ukraine, and I am sure that this united effort in the international arena, bringing together all democratic countries, can still allow us to halt this aggression."
Earlier, President Vladimir Putin said he would discuss relations with Ukraine, the United States and the European Union at a meeting with senior Russian security officials on Thursday, Russian news agencies reported.
"Let's think together about how to conduct relations with our partners and friends in Ukraine and with our other partners in Europe and the United States," Interfax quoted Putin as saying at the beginning of a meeting of his presidential Security Council.
This as the Russian Defense Ministry said that about 8,500 Russian troops are taking part in military exercises near the border with Ukraine involving artillery and multiple rocket launchers.
A statement on the ministry's website confirmed that the exercises had begun at bases in the Southern Military District but did not say how long they would last.
The exercises are likely to cause concern in Ukraine because of the political standoff between Kiev and Moscow over Ukraine's Crimea region, which is now in the hands of Russian forces.
For his part, Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry discussed proposals for resolving the crisis in Ukraine during a telephone conversation, the Russian Foreign Ministry said.
Lavrov and Kerry, who are due to meet in London on Friday, discussed "the situation in Ukraine, taking into account existing Russian and U.S. proposals to normalize the atmosphere and provide for civil peace", the ministry said.
NATO:
Russia's top general discussed the situation in Ukraine with the chairman of NATO's Military Committee by telephone on Thursday, the Interfax news agency cited the Russian Defence Ministry as saying.
The chief of general staff of the Russian armed forces, General Valery Gerasimov, discussed "the state of Russia-NATO relations and the current situation in Ukraine" with NATO General Knud Bartels, the report said.
Germany
Germany assumes that this weekend's referendum in Crimea will be followed by steps to absorb the region into Russia, German Foreign Minister Frank-Walter Steinmeier said on Thursday, and if there is no change in direction the European Union will be forced to consider a further, third stage of sanctions.
Speaking to reporters after meeting counterparts from central Europe, Steinmeier said Russia had so far rebuffed all European proposals to defuse the standoff in Crimea.
He said European states over the weekend would draw up a list of Russians who will be subject to visa restrictions and asset freezes as part of initial sanctions already agreed within the European Union.
This comes as German Vice-Chancellor Sigmar Gabriel said it was in Vladimir Putin's hands whether the Cold War era returned and a weekend referendum in Crimea, likely to violate Ukraine's territorial integrity, would bring a second stage of EU sanctions on Moscow.
"Germany is doing everything to prevent a third round of sanctions against Russia," he said, but added that at the same time if diplomacy failed, Europe should not hesitate to impose a third round of massive economic sanctions of Russia.
Earlier, German Chancellor Angela Merkel said in a speech in parliament that instead of acting as a partner for stability in the Ukraine crisis, Russia had sought to exploit the weakness of its neighbor.
"The territorial integrity of Ukraine cannot be called into question," she said, making clear that the situation in Ukraine's southern region of Crimea was not comparable to the case of Kosovo in the Balkans.
Merkel said that Russia risked "massive" political and economic damage if it refused to change course on Ukraine.
"Ladies and gentlemen, if Russia continues on its course of the past weeks, it will not only be a catastrophe for Ukraine," she said, using her strongest rhetoric since the start of the crisis.
"We would not only see it, also as neighbors of Russia, as a threat. And it would not only change the European Union's relationship with Russia. No, this would also cause massive damage to Russia, economically and politically."
IMF:
The International Monetary Fund has made good progress in its fact-finding mission in Kiev and will soon discuss Ukraine's economic situation with IMF management, a Fund spokesman said.
A team from the IMF arrived in Kiev last week to assess the country's economic situation and discuss a possible bailout program. Ukraine's new government has said it desperately needs cash to cover expenses and avert a possible default.
"My understanding is that ... the discussions in Kiev had made good progress, there has been a very good exchange of views," IMF spokesman Gerry Rice told reporters. He said the mission would return to Washington soon, possibly on Friday.
OSCE:
Russia has voiced support for the deployment of an OSCE monitoring mission in Ukraine, including Crimea, the chairman of the European security group said on Thursday, calling this a possible "big step forward."
"The Russian Federation supported the idea of a rapid approval and rapid deployment of a special monitoring mission for Ukraine," Thomas Greminger, Switzerland's ambassador to the Organization for Security and Cooperation in Europe, told reporters after a meeting of OSCE envoys in Vienna.
REUTERS