Ukranian politician Vladimir Rybak was killed

After two men, one a local politician, were "tortured to death", Ukraine's acting president has ordered the relaunch of military operations against pro-Russian militants in the east.

Olexander Turchynov said the body of politician Vladimir Rybak was found near rebel-held Sloviansk.

"The terrorists who effectively took the whole Donetsk region hostage have now gone too far", he said.

The move came as US Vice-President Joe Biden was visiting Ukraine. In another US move, Washington is sending 600 troops to take part in Nato exercises in the three Baltic states and Poland.

Announcing the decision to reactivate the military operation in eastern Ukraine, Mr. Turchynov said in a statement: "I call on the security bodies to resume and carry out successful anti-terrorist measures aimed at defending Ukrainian citizens living in the east of Ukraine against terrorists".

Mr. Rybak, whose body was found on Tuesday, was described as a local councillor for the Fatherland party in the nearby town of Horlivka. The other man killed has not yet been publicly identified. Mr. Rybak had gone missing recently and, according to police, his body was found in a river.

"These crimes are being committed with the full support and connivance of the Russian Federation", Mr. Turchynov said.