Ukraine relaunched military operations against pro-Kremlin separatists late Tuesday, hours after US Vice President Joe Biden ended a two-day Kiev visit in which he warned Russia over its actions in the former Soviet republic.The US Defence Department at the same time announced it was sending 600 US troops to neighbouring Poland and to Baltic countries for “exercises”. Russia already has tens of thousands of its troops massed on Ukraine’s eastern border. The latest moves underscored the severity of the crisis that has brought East-West relations to their most perilous point since the end of the Cold War.Ukraine’s acting president, Oleksandr Turchynov, late Tuesday said he was ordering the military to restart operations against the rebels after the discovery of two “brutally tortured” bodies in the eastern rebel-held town of Slavyansk. One of them, he said, was that of a recently kidnapped local councillor from a nearby town who belongs to his party.Turchynov earlier Tuesday said the rebels’ refusal to comply with an accord signed last week by Kiev, Moscow and the West to de-escalate the crisis “puts a cross” through the agreement.A further indication of a slide back towards violence, which many fear could tip into civil war, came when a Ukrainian reconnaissance plane was hit by gunfire while flying above Slavyansk.The Antonov An-30 propellor-driven plane received several bullet impacts, but safely made an emergency landing and none of its crew members was hurt, the defence ministry in Kiev said.The Organisation for Security and Cooperation in Europe, which has monitors in the country, also said that rebels had abducted a police chief in the town of Kramatorsk — calling it the sort of “provocative” action that “can only worsen the existing tensions and contribute to further violence”. Pro-Moscow militants had taken over Kramatorsk’s police station late Monday, extending their grip from the already occupied town hall.Kiev, Washington and many EU countries see Moscow as pulling the strings in the Ukrainian separatist insurgency.Biden, in his news conference in the capital after meeting Kiev’s leaders, warned Russia of isolation if it continues to try to “pull Ukraine apart”, underlining a US threat to impose more sanctions on Moscow. “We have been clear that more provocative behaviour by Russia will lead to more costs and to greater isolation,” said the vice president.But Russia says Kiev’s leaders — whom it regards as illegitimate — are to blame for the collapse of the accord. It says ultra-nationalists who were involved in months of Kiev protests that ousted pro-Kremlin president Viktor Yanukovych in February killed rebels in an attack Sunday near the eastern town of Slavyansk. A funeral for the militants was held on Tuesday. Bells rung loudly from Slavyansk’s Orthodox church and women wept as three coffins were carried out.Biden, after meeting Ukraine’s leaders in Kiev, called on Russia to pull back its forces from Ukraine’s border, and to reverse its annexation last month of Ukraine’s Crimea peninsula.“We in the United States stand with you and the Ukrainian people,” Biden said in a joint news conference with Ukrainian Prime Minister Arseniy Yatsenyuk. He added that the United States was stepping up to help Ukraine lessen its dependence on Russian gas, fight corruption, and prepare for a May 25 election to choose a new president.Yatsenyuk responded that Kiev valued the US support against what he said was a Russia “acting like an armed bandit”.In Moscow, Russian Prime Minister Dmitry Medvedev dismissed the US threat of new sanctions.“I am sure we will be able to minimise their consequences,” he said in a televised speech to the Russian parliament.However he acknowledged that Russia’s economy was facing an “unprecedented challenge”.Russia’s finance ministry said Monday the energy-rich nation could tip into “technical recession” over the next three months. Last week it warned Russia was facing the toughest economic conditions since 2009, when a serious slowdown occurred.- EU divided on further sanctions -The European Union, meanwhile, is divided on going further with its own sanctions on Moscow, with some member states worried that increased punishment could jeopardise supplies of Russian gas.As the crisis deepens, the insurgents in Ukraine’s east remain firmly entrenched in public buildings they have occupied for more than a week.In the town of Lugansk, close to the Russian border, protesters pledged to hold their own local referendum on autonomy on May 11, the Interfax-Ukraine news agency reported. Although highly trained military personnel, whose camouflage uniforms are stripped of all insignia, are helping the rebels secure the some 10 towns they hold, Russian President Vladimir Putin denies they are Russian special forces.But the US State Department released images Monday it claims proves some of the armed “separatists” in Ukraine are actually Russian military or intelligence officers. In a separate development, Sweden, which is not a NATO member, announced Tuesday it was increasing defence spending because of the “deeply unsettling development in and around Ukraine”. It plans to boost its fleets of fighter jets and submarines.