VLADIVOSTOK, Russia, Sept 2 (Reuters) - The Kremlin said on Thursday that U.S. military assistance to Ukraine could make Kyiv behave unpredictably and dangerously in the conflict in its east, and expressed regret at a U.S.-Ukrainian friendship it said was motivated by opposition to Russia. U.S. President Joe Biden told Ukrainian President Volodymyr Zelenskiy in Washington on Wednesday that the United States was "firmly committed" to Ukraine"s territorial integrity and offered $60 million in new security aid. read more Ukrainian troops have battled Russian-backed forces in its eastern Donbass region since 2014, a conflict Kyiv says has killed 14,000 people. Kremlin spokesman Dmitry Peskov raised concerns about plans for U.S. military aid in comments to reporters in the city of Vladivostok in Russia"s far east. "We believe this could potentially cause unpredictable actions by the Ukrainian side in terms of attempting to resolve the ... Ukrainian conflict ... by force. This is very dangerous," Peskov said. ".... to put it simply, we"re talking about a Ukrainian-American friendship against Russia. That is to say, they"re friends not for themselves, but against Russia. This ... can only be a cause for regret," he said. He voiced Moscow"s long-standing opposition to Kyiv"s desire to join the NATO military alliance, noting comments made during Zelenskiy"s trip. Zelenskiy has said Ukraine had done everything necessary to earn a NATO membership plan, which Kyiv sees as a vital deterrent against Russia. read more NATO believes Ukraine needs to adopt more political reforms before gaining membership. Russia early this year built up tens of thousands of soldiers near Ukraine, alarming Kyiv and the West before ordering them back to base. read more