Ukraine retook the airfield in the Ukrainian town of Kramatorsk from pro-Russian militants, acting president Oleksander Turchinov said on Tuesday in a statement from his office.
Meanwhile, a Reuters correspondent heard several shots fired from inside Kramatorsk air base as a crowd of pro-Russian locals approached the gate of the facility that appeared to be under the control of Ukrainian forces.
There was no sign of casualties and no gunfire or fighting during the 40 minutes before the shots were fired, the correspondent said.
This comes as Ukrainian troops disembarked from at least two helicopters at an airfield on the outskirts of the eastern Ukrainian city of Kramatorsk, a Reuters witness said.
The defense ministry was quoted as saying it had launched a "special operation" against pro-Russia separatists who seized buildings in the town on Saturday.
Earlier, Ukrainian police said that pro-Russian separatists had voluntarily surrendered the police headquarters in the city of Kramatorsk which was taken by armed militants on Saturday.
"They left of their own accord," Igor Dyomin, a spokesman for the Donetsk region police, told Reuters.
This as, US President Barack Obama warned Russian President Vladimir Putin in a call that Moscow would face further costs if its actions in Ukraine persisted, the White House said in a statement.
"The president expressed grave concern about Russian government support for the actions of armed, pro-Russian separatists who threaten to undermine and destabilize the government of Ukraine," the statement said.
"The president noted Russia's growing political and economic isolation as a result of its actions in Ukraine and made clear that the costs Russia already has incurred will increase if those actions persist," it said.
SBU:
Ukraine's state security service has opened a criminal case against officials at an unnamed Russian bank for "providing financing to terrorists," the SBU said in a statement on Tuesday.
The SBU said the bank transferred 45 million hryvnia ($3.75 million) between March and April for the financing of militant groups and had transferred between $200 and $500 per day to individual militants.
It said the bank had transferred funds to militants involved in the takeover of SBU offices in the eastern Ukraine city of Luhansk.
UN
Russia sharply criticized a U.N. human rights report that said ethnic Russians in eastern Ukraine have falsely claimed to be under assault to justify Russian intervention, saying it was "one-sided, politicized and not objective".
"One gets the impression that the report was fabricated to correspond with conclusions formed in advance," the Russian Foreign Ministry said of the document, issued after two visits to Ukraine last month by a U.N. assistant secretary-general.
This comes as a report by the UN human rights office said that Ethnic Russians in eastern Ukraine have falsely claimed to be under attack to justify Russian involvement.
"Although there were some attacks against the ethnic Russian community, these were neither systematic nor widespread," said the report, which follows two visits to the country last month by Assistant Secretary General for Human Rights Ivan Simonovic.
"Photographs of the Maidan protests, greatly exaggerated stories of harassment of ethnic Russians by Ukrainian nationalist extremists, and misinformed reports of them coming armed to persecute ethnic Russians in Crimea, were systematically used to create a climate of fear and insecurity that reflected on support to integration of Crimea into the Russian Federation."
Naftogaz:
Ukrainian state energy company Naftogaz said it is ready to pay in full for imported gas from Russia at $268.5 per 1,000 cubic meters, much lower than $485 Moscow has set for the second quarter.
Naftogaz said it had sent the similar proposal to Russia's state-controlled gas producer Gazprom on April 4, but has not received an answer.
"Naftogaz has repeatedly sent its proposal about immediate payments for full volumes of imported gas if there is agreement (setting) the proce for Russian gas at the level of $268.5," Naftogaz said.
Gazprom:
Alexei Miller, The head of Gazprom told European Union Energy Commissioner Guenther Oettinger on Tuesday that the Russian company "is a reliable supplier of gas to the European market and will remain one going forward," Gazprom said in a statement.
Amid a tense political dispute with Kiev and the West, Russia has threatened to decrease gas supplies to transit nation Ukraine if it continues to fail to pay its debts, but Moscow has also sought to reassure European consumers it will abide by all contracts. Gazprom said Ukraine now owes $2.2 billion.
International positions:
Russia has deliberately pushed Ukraine "to the brink" in recent days and increased the risk of violent confrontation there, British Foreign Secretary William Hague will say on Tuesday in a speech in London.
Hague's comments, released in advance by his office, come after Russia declared Ukraine to be on the verge of civil war and as Kiev said an "anti-terrorist operation" against pro-Moscow separatists was under way.
For his part, German Economy Minister Sigmar Gabriel said Moscow must show it is serious about a de-escalation in Ukraine by pledging concrete steps to ease tensions in four-way talks scheduled for Thursday in Geneva.
"These talks are long overdue ... We expect that Russia will take serious and publicly visible steps in these talks towards de-escalation. It's in Russia's hands to prevent a further escalation that would be linked to economic sanctions," Gabriel told reporters.
Also on Tuesday, Russian President Vladimir Putin told U.N. Secretary General Ban Ki-moon that the United Nations and the international community should condemn the use of force by the Ukrainian authorities in eastern Ukraine, the Kremlin said.
In a telephone conversation with Ban, Putin "underscored that the Russian side expects a clear condemnation from the United Nations and the international community of these anti-constitutional actions", a Kremlin statement said.
Russia also said it was deeply concerned over reports of casualties in eastern Ukraine, where Kiev has launched an operation against pro-Russian separatists.
"The reports we are getting cause deep concern. To all appearances, events are beginning to develop under the worst case scenario," Konstantin Dolgov, the Russian foreign ministry's human rights representative, was quoted by state news agency RIA as saying.
In turn, Russian President Vladimir Putin's spokesman said that there are no Russian military forces in eastern Ukraine and that any claims of their presence there are absurd.
"This is an absurd assertion, there are no Russian troops there," the spokesman, Dmitry Peskov, told a conference call. He suggested that Western governments were deliberately ignoring Russian assurances on this score, saying "one can only express puzzlement that they prefer not to hear all the statements of the Russian side."
Earlier, Russian Foreign Minister Sergei Lavrov said he welcome signs the government in Kiev was ready for dialogue with separatists in eastern Ukraine, calling it "a step in the right direction", the Interfax news agency reported.
Speaking during a visit to Beijing, Lavrov said Kiev's apparent willingness to "resolve through negotiations all the problems relating to the legal demands of the inhabitants of the south-east regions of Ukraine, is certainly a step in the right direction, albeit very belated."
REUTERS