KIEV, April 22 - Acting President Oleksandr Turchynov called on Tuesday for government forces to re-launch an offensive against pro-Russian rebels after a local politician from his own party was found dead with signs of torture.

Kiev's first push failed last week to retake one of the towns in the mainly Russian-speaking east occupied by the separatists, and its military has largely suspended operations since the United States, Russia, Ukraine and European Union signed a deal in Geneva last week intended to calm the crisis.

But the agreement is already in trouble, with Washington and Moscow putting the onus on each other on Tuesday to ensure that it is implemented, including a stipulation that the rebels must disarm and leave the government buildings they have occupied.

In an appeal that may complicate European efforts to mediate the crisis, Turchynov said two "brutally tortured" bodies had been found near Slaviansk, the objective of the failed Ukrainian army offensive. One was that of Volodymyr Rybak, a member of Turchynov’s Batkivshchyna party, who had recently been abducted by "terrorists", he said in a statement carried by Reuters.

"These crimes are being carried out with the full support and indulgence of the Russian Federation," he said. "I call on the security agencies to re-launch and carry out effective anti-terrorist measures, with the aim of protecting Ukrainian citizens living in eastern Ukraine from terrorists."

Police said the body of a man who suffered a violent death had been found in a river. It resembled Rybak, a local councilor in the town of Horlivka, near the regional capital of Donetsk, but formal identification would need further work, they added.

Batkivshchyna is led by Yulia Tymoshenko, a former prime minister who is running in a presidential election scheduled for May 25.

Ukraine's poorly resourced forces had previously shown little sign of taking on the gunmen who started occupying towns and public buildings two weeks ago. Turchynov’s call may not lead to much more action but could fuel recriminations between Moscow and Kiev about who is failing to honor the deal.

U.S. Vice President Joe Biden told Russia on Tuesday that "time is short" for action on defusing the crisis, but Moscow refused to be rushed, saying it could handle any tougher economic sanctions the West might impose.

Speaking on a visit to Kiev, Biden called on Moscow to pull back troops built up on Ukraine's borders and persuade the separatists to disarm.

"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," he told a news conference. "We will not allow this to become an open-ended process. Time is short in which to make progress."

The United States has repeatedly warned Russia it faces "mounting costs" if it fails to ensure full implementation of the Geneva agreement. (rt/ez)