Pro-Russia gunmen holding a group of international observers captive in Ukraine say they are willing to carry out a prisoner swap.
The self-proclaimed separatist leader in the city of Slovyansk said he was willing to trade the Organisation for Security and Cooperation in Europe (OSCE) monitors for anti-government activists detained by Kiev.
Separatist leader Vyacheslav Ponomaryov told reporters on Saturday that they had not planned to take the monitors, who the pro-Kremlin group accuses of being "NATO spies."
"That was not our plan to take prisoners for a swap. But you understand that prisoners have always been coins to exchange during times of war. It's an international practice to swap prisoners. There is nothing scary about it," he said.
International efforts are still under way to secure the release of a 13-member mission from the OSCE held hostage in Slovyansk since Friday.
Denis Pushilin, the self-styled leader of the city of Donetsk, also said the monitors would only be released in exchange for men detained by Ukrainian forces.
Meanwhile, Russia's envoy to the OSCE said Moscow would "take all possible steps in this case".
"We believe that these people should be released as soon as possible," Andrei Kelin said.
Russian's foreign ministry also said Moscow was "taking measures" to resolve the situation but blamed the Ukrainian authorities for the hostage crisis.
"They were invited by the Ukrainian authorities" and their safety "rests fully with the receiving side", the foreign ministry in Moscow said.
Ponomaryov described the detained observers as "captives" and said that they were officers from NATO member states.
"As we found maps on them containing information about the location of our checkpoints, we get the impression that they are officers carrying out a certain spying mission," he said.
Germany's Defence Ministry said it had had lost contact with the team, which it said also included five Ukrainians.
Al Jazeera's Barnaby Philips, reporting from Donetsk, said that a team was en route to negotiate the release of the observers.
"Some sort of OSCE mediation is on its way here to try to talk about this situation," he said.
The foreign observers were sent to Ukraine to monitor an April 17 accord signed in Geneva between Russia, Ukraine, the United States and the European Union that was meant to de-escalate the dangerous crisis in the ex-Soviet republic.
Despite assurances from Russia that it would work to secure the release of the team, interim Ukrainian Prime Minister Arseniy Yatsenyuk said the seizure was "another proof and evidence that these so-called peaceful protesters with Russian ideas are terrorists".
In a briefing with reporters, he lashed out at Moscow, saying Russian military aircraft violated Ukrainian air space late on Friday.
"Russian military aircraft today overnight crossed and violated Ukrainian airspace seven times. The only reason is to provoke Ukraine to start a war," he said.
Russia's defence ministry, however, denied claims that its planes had made any such violation.
"Russia's airspace monitoring systems have not registered any violations of air borders of the states adjacent to Russia, including Ukraine," the defence ministry said in a statement carried by the state ITAR TASS news agency.