The United States signed an agreement on Wednesday to provide $2 billion in loan guarantees to help war-torn Ukraine with "near-term social spending" in 2015 and said it was prepared to step up economic sanctions against Russia if necessary.After signing the deal with Ukrainian Finance Minister Natalia Yaresko, U.S. Treasury Secretary Jack Lew criticized what he called "Russian aggression", a reference to Moscow's support for separatists battling Kiev's forces in eastern Ukraine which has triggered the Western sanctions on Moscow."We remain prepared to do more (on sanctions) if necessary. To that end, we will continue to work with our allies to increase the pressure on Russia," Lew told reporters at the signing ceremony.Lew added that the sanctions could be eased if Russia abided by the terms of the Minsk agreements signed last September which called for a ceasefire and the withdrawal of Russian fighters and military equipment from Ukraine. Like other major donors to Ukraine, Lew said the U.S. deal was contingent on the ex-Soviet republic continuing with fiscal and anti-corruption reforms and remaining on track to meet the conditions of its loan program with the International Monetary Fund. IMF officials are now in Kiev negotiating a bail-out package, currently worth $17 billion, which Ukraine's pro-Western government hopes will be expanded to help it handle crippling external debt repayments due this year.U.S. lawmakers passed a bill dubbed the Ukraine Freedom Support Act in December 2014. The bill covers further economic sanctions against Russia and the delivery of up to $350 million worth of U.S. military hardware including anti-tank weapons, ammunition and troop-operated surveillance drones to Ukraine. These sanctions would be expected to hit the defense and energy sectors of the Russian Federation. Russian producers, transferers, or brokers of defense articles are expected to be hit by the sanctions.Moscow denies Western and Ukrainian accusations that it has sent regular forces into eastern Ukraine. Russia's increased militarization of the rebel-held areas in the Donbass region in eastern Ukraine, and its explicit support to pro-Russian separatists seeking a regional leadership close to Russia has long been condemned by the United States, together with the European Union, imposed series of tightened economic sanctions on Russian individuals and large companies.Following the bloody upsurge around the southeastern port of Mariupol, the EU foreign ministers drew up possible further measures such as expanding a blacklist of individual sanctions over the Ukraine crisis.The months-long conflict in eastern Ukraine has come at the cost of an increasingly high death toll, with a large increase in the numbers of internally displaced people. More than 5,000 people were reportedly killed during heavy clashes in rebel-held areas, according to U.N. figures.