The United States and its European allies are considering the use of naval assets to deliver humanitarian aid to Libya and to block arms shipments to the government of Moammar Gaddafi, even as they weigh the legality of imposing a no-fly zone without United Nations authorization, according to U.S. and European officials.

NATO military officials began briefing governments Tuesday night on a range of options that will be presented to defense ministers in Brussels on Thursday.

The Obama administration, NATO and other international organizations are united in their belief that any military intervention in Libya would require some international backing. But with a U.N. mandate far from assured, those considering some form of intervention - including the United States, Britain, France and Italy - are looking for alternative support, officials said.

Officials, saying international support could come from regional blocs, noted that NATO's air attacks on Serbia in 1999 came without U.N. backing.

"If you have [support from] the Arab League, the African Union, NATO and potentially the European Union, you have every country within 5,000 miles of Libya," a NATO official said. "That gives you a certain level of legitimacy."

The intense international deliberations came as troops loyal to Gaddafi continued to besiege the rebel-held city of Zawiyah, 27 miles west of Tripoli, for a fifth day on Tuesday, with rebel officials there citing a mounting toll - dozens dead and hundreds wounded, including women and children.

In Ras Lanuf, about 400 miles east of the capital, Gaddafi loyalists were engaged in fierce fighting with rebels who had hoped to march on Sirte, Gaddafi's home town and a strategically vital city still under tight government control.

Gaddafi made a surprise appearance at a hotel hosting foreign correspondents, arriving just before midnight, AP reported. He raised his fist in the air as he walked from his car to the hotel, then went into a room for about an hour to give exclusive television interviews. He did not speak to reporters waiting outside.

The Libyan leader told a Turkish television crew that Libyans would fight back if Western nations imposed a no-fly zone, and said such restrictions would prove the West's real intention was to seize his country's oil wealth.

"Such a situation would be useful," Gadhafi said, according to AP. "The Libyan people would understand their real aims to take Libya under their control, to take their freedoms and to take their oil and all Libyan people will take up arms and fight."

As they weigh the prospect of intervention, the Obama administration and European governments are continuing to size up the Libyan opposition. "We feel that we don't really understand who they are yet," said a senior European diplomat who, like other officials interviewed, spoke on the condition of anonymity to discuss closely held deliberations. "They are more fractured and complicated and less well-coordinated than we would like."

France and Italy said they were in direct conversations with some opposition figures, and the State Department said it had held face-to-face meetings and telephone conversations in Rome and Cairo with members of the Benghazi-based National Transitional Council.