Acting Ukrainian President Oleksandr Turchynov on Wednesday ordered that a military operation against armed pro-Russian protesters in the country's east resume, as Russia's foreign minister warned of "retaliation" if Russians' rights were violated.
The resumption of the military operation came after two dead bodies were found near the town of Raigorodok next to Slovyansk, which is effectively controlled by armed separatists, in the Donetsk region.
One of the victims has been identified as a member of a local municipal council, Volodymir Rybak, and the other body has not yet been identified.
Rybak, of the liberal Batkivshchina party, a member of the Horlivka city council, was kidnapped earlier this month.
"Traces of torture are visible on their bodies: their bellies were ripped open when they were still alive, then their backpacks were filled with sand and tied to their backs, and they were thrown into the water alive," Stanislav Rechinsky, an assistant to Ukraine's interior minister, said Wednesday.
"According to experts, this style is characteristic of Russian special forces and paramilitary groups like the Cossacks."
While the full circumstances of the killings remain unknown, Turchynov made clear that he believed pro-Russian separatists were involved.
"I call on the security agencies to relaunch and carry out effective counter-terrorist measures, with the aim of protecting Ukrainian citizens living in eastern Ukraine from terrorists," Turchinov said in a statement posted on the Ukrainian parliament's website Wednesday.
The first Ukrainian counter-terrorism operation, launched on April 13, had been suspended for the Easter holiday.
"These crimes are being committed with the full support and indulgence of the Russian Federation," Turchinov said.
Turchynov also said pro-Russian militants had violated the Geneva agreement, which was concluded last week by Russia, the U.S., Ukraine and the EU in an effort to stabilize the situation in eastern Ukraine.
Russia, for its part, pointed the finger at the West as tensions boiled over on Wednesday, with Lavrov accusing a military contractor of involvement in Ukraine violence.
"There is no reason not to believe that the Americans are running the show," Lavrov told RT television on Wednesday, citing as evidence U.S. Vice President Joe Biden's ongoing visit to Ukraine.
Lavrov called for an investigation into unconfirmed reports that U.S. employees of the private military contracting firm Greystone have taken part in the Ukrainian government's "anti-terrorism" operation. Greystone has denied that claim.
Lavrov also accused both the U.S. and Ukraine of violating the Geneva agreement and said the Kremlin was unable to make pro-Russian protesters comply with the deal, a demand the West has repeatedly made of Russia in recent days.
"We do not have any moral authority or any tools to influence southern Ukraine," Lavrov said.
Lavrov also hinted that Russia would hit back if its interests were violated by the events in Ukraine.
"If our interests, our legitimate interests, the interests of Russians have been attacked directly, like they were in South Ossetia, for example, I do not see any other way but to respond in accordance with international law," he said, referring to the 2008 war between Russia and Georgia over the latter's breakaway republic of South Ossetia.
Volodymyr Fesenko, head of the Kiev-based Penta political research group, said that a full-fledged Ukrainian military operation was unlikely, however, and that he expected the measures to be limited to authorities blocking pro-Russian protesters from infiltrating other regions and conducting small ad hoc operations wherever necessary.
It would be very difficult for Ukraine to conduct counter-terrorism measures in eastern Ukraine because the local population is mostly hostile to the central government, Fesenko said. In addition, he said, the local police are demoralized and there are few effective units left in the Army and Special Forces.
"The new government has neither power nor resources to conduct a full-fledged counter-terrorism operation," he said.
"Local police are reluctant to take action because they don't even know which side will win, and the army has effectively been destroyed in recent years," he said.