Ukraine has asked Moscow, under European OSCE security arrangements, to explain and give details of its military exercises near the border within 48 hours, the Foreign Ministry said on Thursday.
Ukraine's acting president Oleksander Turchinov also called on Russia to pull troops back from their border, stop interfering in Ukraine's internal affairs and end its "blackmail".
Turchinov broadcast his brief address to the nation after Russia said it had begun military exercises near the border in response to escalation by Ukraine.
Russia started military drills near the Ukrainian border on Thursday in response to operations by Ukrainian forces against pro-Russian separatists and NATO exercises in eastern Europe, Defense Minister Sergei Shoigu was quoted as saying by the Interfax news agency.
"If this military machine is not stopped, it will lead to greater numbers of dead and wounded. Planned exercises by NATO forces in Poland and the Baltic countries do not foster normalization of the situation surrounding Ukraine, either," Shoigu was quoted as saying. "We are forced to react to such a development of the situation."
This comes after Ukrainian troops withdrew from a checkpoint they had taken over earlier in the day north of the eastern city of Slaviansk and pro-Russian separatists moved back in and began to reinforce the position with sandbags.
A Reuters journalist said the troops, with armored vehicles, pulled back after about two hours at the checkpoint on a road near the village of Khrestyshche.
Earlier, Ukraine's interior ministry said its forces had killed "up to five" militants in the separatist-controlled town of Slaviansk, in the east of the country.
A ministry statement said that during an "anti-terrorist operation," its forces, supported by the army, removed three illegal checkpoints manned by armed groups in the northeastern part of the city.
During the armed clash up to five terrorists were eliminated," it said. One person had been wounded on the side of government forces, it added.
American journalist:
American journalist Simon Ostrovsky has been released in eastern Ukraine, said online news site Vice News, for whom he was working in the city of Slaviansk when he was held by pro-Russian separatists on Monday.
"Vice News is delighted to confirm that our colleague and friend Simon Ostrovsky has been safely released and is in good health," read a statement on its Web site on Thursday.
No information was immediately available from the separatists, who have said they hold several people.
IMF:
The International Monetary Fund said on Thursday that Ukraine's government had provided the documentation needed to show whether it had met conditions for a financial aid package and the Fund's board would meet on April 30 to review and consider the matter.
The IMF tentatively agreed in late March to provide a $14 billion-$18 billion two-year bailout to help Ukraine recover from months of political and economic turmoil. The IMF board has yet to approve that package.
Reactions:
Russian President Vladimir Putin's spokesman said on Thursday that events in Ukraine, where government forces have conducted operations targeting separatists, raise serious questions about the legitimacy of a Ukrainian presidential vote set for May 25.
"There is no doubt that such a development as criminal actions by those in Kiev ... place the legitimacy of the election scheduled for May in very serious question," Putin's spokesman Dmitry Peskov told reporters.
Earlier, Russian President Vladimir Putin said that sanctions were hurting the Russian economy but that the damage was not critical.
President Putin condemned the use of sanctions as an instrument of interstate policy on Thursday, saying they damage all concerned and reflect badly on those who impose them.
Putin also said that if Kiev authorities have used the army against pro-Russian activists in east Ukraine there will be consequences.
For his part, Russian Foreign Minister Sergei Lavrov said that the Ukrainian authorities must take the first step if a resolution is to be found to the Ukraine crisis.
Lavrov, speaking at a news conference after meeting his Lebanese counterpart, also said the United States should use its influence to persuade Kiev to implement its commitments under an international accord on Ukraine that was signed last week.
Also on Thursday, Czech Prime Minister Bohuslav Sobotka said the Czech Republic and Slovakia are skeptical about imposing broad-based sanctions on Russia over its actions in Ukraine because it could damage economic growth in Europe.
Sobotka said after meeting his Slovak counterpart Robert Fico that any decision on further sanctions should be taken at the level of European heads of state and government and the Czechs would speak against "broad-based" sanctions.
He said both countries supported demands that Russia pulls its troops from the Ukrainian border and did not interfere in preparations for Ukraine's presidential election.
REUTERS