But US Defense Secretary Robert Gates said the US would not have a "pre-eminent role" in maintaining it, and expected to turn over "primary responsibility" within days, perhaps to Britain or France.

US officials have been playing down Washington's role and emphasizing that overthrowing or killing Gadhafi is not the goal of the attacks on Libya.

Mullen told CBS television the end game of the campaign was "very uncertain" and acknowledged it could end in a stalemate.

Gates told reporters: "I think this is basically going to have to be resolved by the Libyans themselves."

In Brussels, NATO envoys failed to agree on any alliance involvement in enforcing the no-fly zone.

NATO members Turkey and Germany have spoken out against the zone.

Turkish Prime Minister Tayyip Erdogan said on Monday that Turkey wants the international military operation against Gadhafi's forces to be concluded as soon as possible so that Libyans can settle their own future.

In Moscow, Russian Prime Minister Vladimir Putin said a UN resolution authorizing military action in Libya resembled "medieval calls for crusades".

"The resolution is defective and flawed," Putin told workers at a Russian ballistic missile factory. "It allows everything. It resembles medieval calls for crusades."

In Cairo, a group of Libyans angry at the international intervention in their homeland jostled UN Secretary-General Ban Ki-moon following a meeting at the Arab League on Monday.

The Libyans, carrying pictures of Gadhafi and banners critical of the US and the UN, blocked Ban's path, forcing him to return to the league and leave from another exit.

AP contributed to this story.

Reuters