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in a nationally televised address, Obama -- accused by many lawmakers of failing to explain the U.S. role in the Western air campaign against Gaddafi's loyalists -- made the case for his decision to intervene militarily in the Libya conflict.

But he also underscored the limits of U.S. Buy nike running shoes onlinemilitary action as he sought to counter criticism that he lacked clear objectives and a credible exit strategy in the conflict.

"I can report that we have stopped Gaddafi's deadly advance," Obama told military officers at the National Defense University in Washington, 10 days after ordering U.S. participation in Western-led air strikes.

"We will deny the regime arms, cut off its supply Buy nike running shoes onlineof cash, assist the opposition, and work with other nations to hasten the day when Gaddafi leaves power," Obama said.

But he added that "it may not happen overnight" Buy nike running shoes onlineand acknowledged that Gaddafi may be able to cling to power. "Broadening our military mission to include regime change would be a mistake," he said.

Obama spoke on the eve of a 35-nation conference in London to tackle the crisis in the North African oil-exporting country and weigh political options for ending Gaddafi's 41-year rule.

Obama's challenge was to define the limited purpose and scope of the U.S. mission in Libya for Americans preoccupied with domestic economic concerns and weary of costly wars in two other Muslim countries, Iraq and Afghanistan.