British forces could be in action over Libya as early as Friday

British forces could be in action over Libya as early as Friday, if a UN resolution is agreed, a senior government source has told the BBC.

BBC political editor Nick Robinson said the source stressed talks were continuing and it could take longer but would be within days of a yes vote.

The UN Security Council is expected to vote on whether to authorise a no-fly zone in Libya within hours.

Britain's ambassador to the UN said there would be a vote at 2200 GMT.

The UK, France and Lebanon drafted the resolution but others on the Security Council are wary of a no-fly zone.

Downing St said Prime Minister David Cameron had called Arab, African and European leaders to "make the case for strong action" by the UN and will continue making calls on Thursday evening.

A Foreign Office spokesman told the BBC that anything short of a strong comprehensive resolution on Libya would be considered "too weak" by the British government, which would not be satisfied by a resolution calling for a ceasefire.