Ukraine vows to bring peace to east
Ukrainian forces will continue their offensive against rebels until peace and order are restored in the east, the interim defence minister has said.
Fighting has intensified around the town of Sloviansk where pro-Russian rebels shot down an army helicopter on Thursday, killing 12 troops.
Dozens of separatists died on Monday in a battle at Donetsk airport.
Russia has again called for Ukraine to stop its military campaign against the pro-Moscow rebels.
President Vladimir Putin said the "bloodshed" had to be stopped, in a phone conversation with French President Francois Hollande on Friday.
"Putin noted the need for the authorities in Kiev to immediately halt the violence, and for the start of direct dialogue between Kiev and representatives of the country's south-eastern regions," the Kremlin said in a statement.
Interim Defence Minister Mykhailo Koval earlier told reporters that Ukrainian forces would continue operations in border areas "until these regions begin to live normally, until there is peace", the Reuters news agency reported.
And he again accused Russia of backing the rebels - a claim Moscow denies.
President-elect Petro Poroshenko has said Ukraine will punish the "bandits" who shot down the helicopter. Among those killed was Maj Gen Serhiy Kulchytskiy, head of combat and special training in Ukraine's National Guard.
Debt partially paid
The leader of the self-declared Donetsk People's Republic, Alexander Borodai, told Russia's TV Rain that the only condition for negotiations with Kiev was the withdrawal of its troops from the territories of Donetsk and Luhansk.
And he denied any knowledge of the whereabouts of a team of monitors from the Organization for Security and Co-operation in Europe (OSCE), held by separatists. The self-proclaimed mayor of Sloviansk has said they will be freed soon but nothing has been heard of them since Monday.
A second group of observers, based in Luhansk, remains unaccounted for.
Separatists there told the Interfax-Ukraine news agency they had released the team, but the OSCE has put out a statement saying it lost contact with the observers at 19:00 local time (16:00 GMT) on Thursday.
Pro-Russian separatists in the regions of Donetsk and Luhansk declared independence after referendums on 11 May, which were not recognised by Kiev or its Western allies.
The rebels took their cue from a disputed referendum in Crimea, which led to Russia's annexation of Ukraine's southern peninsula.
Up to 33 Russian nationals were among the dozens of rebels killed in fighting around Donetsk airport on Monday.
US Secretary of State John Kerry said there was "evidence" of Chechens trained in Russia who had come to "stir things up".
Chechnya's president has denied sending troops to Ukraine.
Separately, US officials said Russia had now withdrawn most of its forces from the border with Ukraine, but thousands remained.
In another development, Ukraine has paid part of its gas debt to Russia after talks between both sides and the European Union.
Reports suggest Ukraine has paid state gas company Gazprom $786m (£469m; 576m euros) of the $3.5bn Russia says it is owed.
Gazprom earlier threatened to cut off supplies to Ukraine if it failed to pay in advance for its June supplies.
Russia said negotiations with Ukraine would continue once the payment had been received.