In a nationally televised address, Mr Obama, accused by many lawmakers of failing to explain the US 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 US military 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," Mr Obama told military officers at the National Defense University in Washington, 10 days after ordering US participation in Western-led air strikes.

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

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

Mr 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.

His prime-time speech came a day after NATO agreed to assume full responsibility for military operations in Libya, ending uncertainty about who will take over the lead from US forces. He said the handover will take place on March 30.