U.S. President George W. Bush authorized on Wednesday arms supplies to Kosovo, saying it would "strengthen the security of the United States and promote world peace", the White House website said.
Lavrov told a news conference in Tel Aviv on Thursday evening that sending weapons to Kosovo violated a UN resolution that prohibits weapon supplies to the region, except to UN peacekeeping forces.
"I would not like to think that the supplies are designed to force Serbs and other ethnic minorities to remain in the new illegally formed entity," he also said, adding that, "I do not believe that this will add to stability in the region - it is more likely to have the opposite effect."
Kosovo, with a 90% ethnic Albanian majority, declared unilateral independence from Serbia on February 17. The U.S. and the vast majority of EU states have since acknowledged its sovereignty. Russia, Serbia's traditional ally, has refused to recognize the "world's newest state" and has pledged to block any attempt by Kosovo to seek UN membership.
Earlier this week, violence broke out in the north of Kosovo as rioters attacked UN peacekeepers following the arrests of ethnic Serbs who had seized a UN court building in protest against the province's secession. A Ukrainian peacekeeper was killed and scores of people, both Serbs and UN personnel, were injured.
Earlier on Thursday, Serbia's prime minister blasted the decision to permit U.S. arms deliveries to Kosovo as "another profoundly mistaken step" by Washington.
"Instead of sending more arms to [Kosovo] Albanians, what is really needed is for the U.S. to resume respecting international law and the UN Charter. Kosovo needs new talks and not new weapons," Vojislav Kostunica said.
Russia's envoy to NATO, Dmitry Rogozin, said on Thursday that he would discuss the decision to authorize military assistance to Kosovo at an extraordinary Russia-NATO Council session which could take place on March 28.
Kosovo has been a UN protectorate since 1999, when a NATO bombing campaign of the former Yugoslavia ended a conflict between ethnic Serbs and separatist Albanian forces. Internationally-mediated talks on the region's status broke down last year.