US Secretary of State Hillary Clinton says Muammar Gaddafi's troops "remain a serious threat" to Libyan civilians despite having been pushed back by rebel and allied military action.

Clinton also praised the United Arab Emirates and Qatar for offering "crucial" Arab support for the military coalition in Libya, on a day of intense diplomacy which saw NATO agree to take control of coordinating a no-fly zone.

On the domestic front meanwhile, the White House pushed back at rising domestic political tension on the Libya operation, insisting it had repeatedly consulted key players in Congress before pressing the trigger.

Clinton emerged as the administration's main messenger of the day after talks with President Barack Obama and other senior national security officials on the crisis.

"Gaddafi's troops have been pushed back but they remain a serious threat to the safety of the people," she said, summing up progress after an intense rolling program of air strikes against Gaddafi forces and military assets.

"After only five days we have made significant progress. A massacre in Benghazi was prevented, and Gaddafi's air force and air defences have been rendered largely ineffective."

Clinton also announced that she would attend an international conference in London on Tuesday to decide next steps on the crisis, and reiterated Obama's vow that the US lead in the action would be limited in time and scope.

To that end, NATO announced after intense discussions between key partners in the Libya strike force that it would take over the command and control role of a no-fly zone in Libya designed to protect civilians.

Yet in a sign of differences among key players in the effort, the Western alliance has yet to decide on whether to expand its role to include all necessary means to protect civilians on the ground.

Coalition air strikes in recent days have also targeted Libyan ground forces but Turkey, the only predominantly Muslim member of NATO, remains uneasy about bombing missions on the ground in Libya.

Clinton and the White House also highlighted a boost in Arab support for the mission to shield civilians from Gaddafi's air forces.

"We are deeply appreciative of their continuing contributions including aircraft and pilots from Qatar," Clinton said.

"This evening, the United Arab Emirates announced they are joining the coalition and sending planes to help protect Libyan civilians and enforce the no-fly zone. We welcome this important step," she said.

A US official told AFP on the condition of anonymity that the UAE contributed 12 warplanes.

Clinton said the move underscored "the breadth of this international coalition and the depth of concern in the region for the plight of the Libyan people".

The White House also hailed the "critical participation" of the UAE, which it said had been a leader on the Libya crisis in the Gulf Cooperation Council and the Arab League.

"We look forward to continuing to work closely with the UAE and all of our regional and international partners," said Obama's spokesman Jay Carney.

Clinton added that humanitarian relief is beginning to reach the people who need it in Libya but that it was too early to relax the pressure on Gaddafi.

"This operation has already saved many lives but the danger is far from over.

"As long as the Gaddafi regime threatens its people and defies the United Nations, we must remain vigilant and focused."

Originally published as Gaddafi troops pushed back: Clinton