Ukraine's interim President Oleksander Turchinov has called on security personnel to resume the "anti-terror" operation against pro-Russian protesters after finding the bodies of two Kiev officials.

The bodies, which were found in the eastern Ukrainian city of Slavyansk, were those of local officials. Both had been tortured.

One of the victims has been identified as Volodymyr Rybak, a local councillor representing Turchinov's political party in the town of Horlivka, who went missing recently.

The bodies of Rybak and the second, yet-to-be-identified man were found in a river in the Slavyansk region.

"The opposition Horlivka deputy who fought the separatists, and who was kidnapped in Horlivka...was found dead in Siversky Donets [River] near Slavyansk with a backpack filled with sand around his back and ripped stomach," local lawmaker Oleksandr Bryhynets wrote on his Facebook account.

"Not Fascists, not separatists... it was scoundrels and carrions [murdered him]... who should be obliterated by any means together with their imperial backers...Heroes never die."

Although pro-Russian separatists in the region have denied any link with the killings, Turchinov said: "I demand the resumption of effective counter-terrorism measures to protect Ukrainian citizens in the east from terrorism.

"The terrorists, who basically have taken the entire Donetsk region hostage, have crossed the line with torturing and killing Ukrainian patriots."

'Time is short'

The Ukrainian government has conducted a sweeping "anti-terror" operation, but this largely failed to flush out the separatists occupying government buildings.

The Kiev administration has scaled down its crackdown following the Geneva accord, stipulating that militia forces in the east of Ukraine must leave public buildings and public spaces and turn in their weapons.

Since the agreement was ratified on the evening of 17 April, the western powers and Moscow have been blaming each other for failing to implement it.

"We've heard a lot from Russian officials in the past few days. But now it's time for Russia to stop talking and start acting. We will not allow this to become an open-ended process. Time is short in which to make progress," US Vice President Joe Biden told a news conference as he was wrapping up his official visit to Kiev.