KIEV, Ukraine (AP) -- Ukraine's acting president ordered security forces to resume operations in the country's east on Tuesday after the bodies of two people allegedly abducted by pro-Russia insurgents were found and a military aircraft was reportedly hit by gunfire.
The developments -- just hours after U.S. Vice President Joe Biden left the Ukrainian capital -- raised fears that last week's international agreement on easing Ukraine's crisis was unraveling.
The accord calls for all sides to refrain from violence and for demonstrators to vacate public buildings. It does not specifically prohibit security operations, but Ukraine suspended its so-called "anti-terrorist operation" after it was reached.
Pro-Russia insurgents who have seized police stations and other public buildings in eastern Ukraine are defying the call to vacate, saying they were not party to the agreement by Ukraine, Russia, the United States and the European Union.
In a statement, acting President Oleksandr Turchynov said the two bodies found Tuesday in Slovyansk bore signs of torture. One of the victims was a member of the city council and a member of Turchynov's party, he said.
Terrorists "are beginning to torture and kill Ukrainian patriots. They are impudently rejecting the calls of not only our country but of all the world's society when they demonstratively mock the decisions taken in Geneva," he said.
"These crimes are being done with the full support and connivance of Russia," Turchynov added.
The acting government, which took over after President Viktor Yanukovych fled to Russia in February, says Russia is behind the unrest in eastern Ukraine which it fears Moscow could use as a pretext for an invasion. Last month, Russia annexed Crimea weeks after seizing control of the peninsula.
The Defense Ministry said gunfire hit an observation plane over Slovyansk but the aircraft landed safely without injuries.
Standing alongside Prime Minister Arseniy Yatsenyuk, Biden called on Moscow to encourage pro-Russia separatists in eastern Ukraine to vacate government buildings and checkpoints, accept amnesty and "address their grievances politically."
Biden said Russia needs to act "without delay," adding, "We will not allow this to become an open-ended process."
Yatsenyuk was harsher in his characterization of Russia.
"No country should be able to behave like an armed bandit," he said. "Russia should stick to its international commitments and obligations. They should not behave as gangsters in the modern century."
Also on Tuesday, U.S. Secretary of State John Kerry in a phone call with Russian Foreign Minister Sergey Lavrov also cited mounting evidence that separatists are continuing to increase the number of buildings under occupation and take captive journalists and other civilians. The State Department said Kerry urged Russia to tone down its rhetoric and engage diplomatically in the east with the Ukrainian government and the Organization for Security and Cooperation in Europe.
Meanwhile, hundreds of mourners gathered for the Orthodox funeral services of three pro-Russian militiamen killed in a shootout on Easter Sunday near the eastern city of Slovyansk, which is now under the control of pro-Russian insurgents.
Many used the services to vent their anger at the interim government in Kiev, which they blamed for the deaths. Pro-Russian forces contend that the three men were killed by members of the Ukrainian ultranationalist group Right Sector, which helped to overthrow the government in February
The U.S. has warned that it will quickly order new economic sanctions on Russian officials and entities if Moscow doesn't follow through on the provisions in last week's accord.
Moscow has rejected charges that it was behind the troubles in eastern Ukraine and that it has failed to live up to the Geneva agreement.
"Before putting forth ultimatums to us, demanding fulfillment of something within two-three days or otherwise be threatened with sanctions, we would urgently call on our American partners to fully recognize responsibility for those whom they brought to power and whom they are trying to shield, closing their eyes to the outrages created by this regime and by the fighters on whom this regime leans," Lavrov said.
Biden also announced the United States will provide an additional $50 million to help Ukraine's beleaguered government with political and economic reforms.
The money includes $11 million to help conduct the May 25 presidential election, including voter education, administration and oversight. It also will help fund expert teams from U.S. government agencies to help Ukraine reduce its reliance on energy supplies from Russia. Other technical advisers will help fight corruption.
The White House also announced $8 million in nonlethal military assistance for the Ukrainian armed forces, including bomb-disposal equipment, communications gear and vehicles.