Britain and the US appear to be at odds over the imposition of a no-fly zone over Libya as the UK joined forces with France and Lebanon to press for a fresh UN security council resolution.

Hillary Clinton, the US secretary of state, played down the prospects of a no-fly zone when she declared that there were "other ways" to help the opposition as she warned against unilateral action.

The intervention by Clinton, in an interview on BBC Radio 4's PM programme, came shortly after William Hague said that Britain was prepared to impose a no-fly zone without the authority of the UN.

Meanwhile, Britain summoned the Libyan ambassador to the Foreign Office to emphasise its "profound concern" over reports of the Libyan regime's attacks on civilians.

An FCO statement read: 'We emphasise that perpetrators of violence against civilians will be held to account. We reiterate that the UK and many others in the international community believe Qadhafi must relinquish power immediately."

The different messages were voiced as diplomats from Britain, France and Lebanon in New York sought to win the support of six other members of the security council – and avoid a veto by Russia and China – for a new resolution that would authorise a no-fly zone. The resolution would also tighten the arms embargo on Libya.

Clinton, who said the US "greatly appreciated" the leadership of Britain, France and the Lebanon, admitted that the international community needed to act soon as Muammar Gaddafi's forces recapture large parts of Libya.

"We are well aware that the clock is ticking," the secretary of state said as she praised the Arab League for its "courageous stand" over the weekend in calling for a no-fly zone.

But Clinton made clear the US was highly sceptical about the merits of a no-fly zone. Asked whether there was still time to impose one, she said: "There will be other things considered in addition to a no-fly zone. That will certainly be one of the actions considered. But there are other ways to assist the opposition. All of those are on the table and are being examined."

The secretary of state insisted that an international consensus was necessary as she made clear that no country – or no group of countries – could act alone. "It is important that we get international authorisation through the security council. This cannot be a unilateral action by anyone in Europe or the US or, frankly, anyone in the Arab League. It has to be international and authorised. And then we have to be very clear about what Arab leadership and participation will be.

"We want to get something that will do what needs to be done and can be passed. It won't do us any good to consult negotiate and then have something vetoed or not have enough votes to pass it.

"We are prepared to join an international consensus that comes out of the security council. It is important to underscore that unilateral action is not an option. International action must be the route we take."

The cautious stance of Clinton contrasted with Hague who raised the possibility of imposing a no-fly zone without authorisation from the UN. The foreign secretary told the Commons foreign affairs select committee: "Are there some circumstances in which countries have the right to act and it is legal even without a security council resolution? From all the legal advice I have received, there are circumstances."

Sir Menzies Campbell, the former leader of the Liberal Democrats, asked Hague whether Britain accepted the doctrine of "duty to protect" which could be invoked without a new UN security council resolution if there is an overwhelming humanitarian need. Asked by Campbell whether the doctrine is on the table, Hague said: "It is on the table."

David Cameron urged leaders of countries with seats on the UN security council, most notably Barack Obama, to show some leadership. "Of course there are a wide range of views in the UN," the prime minister told MPs. "I urge all to take the right steps so that we show some leadership on this issue and make sure that we can get rid of this regime."