British and French attack helicopters were used to strike inside Libya for the first time overnight on Saturday, hitting targets in the oil port of Brega as Nato forces stepped up their air war against Muammar Gaddafi.

A Nato-led military alliance extended its mission to protect civilians in Libya for a further 90 days this week, and France said it was stepping up military pressure as well as working with those close to Gaddafi to try to persuade him to quit.

'This was the first operational mission flown by British Army Apaches at sea,' British Secretary of State for Defence Liam Fox said.

'The additional capabilities now being employed by Nato further reinforces the UK's enduring commitment and Nato's determination to... ensure that the people of Libya are free to determine their own future.'

Military analysts say attack helicopters will allow more precise strikes against pro-Gaddafi forces hiding in built-up areas than the high-flying jets used so far, while reducing the risk of civilian casualties.

But given the vulnerability of helicopters to ground fire, their deployment also increases the risk of Western forces suffering their first casualties of the campaign.

Critics of the war have warned of 'mission creep' but Nato has said the use of helicopters would not presage the deployment of ground troops, which Western nations have ruled out.

Now in its fourth month, the Libyan conflict is deadlocked, with rebels unable to break out of their strongholds and advance towards Tripoli, where Gaddafi appears to be entrenched.

The helicopter attacks struck military targets around the eastern town of Brega, location of an oil export terminal.

Rebel forces, who have taken control of the eastern city of Benghazi, swept west through Brega early in the uprising before beating a retreat from near Gaddafi's home town of Sirte in late March. Gaddafi's forces have since dug in around the oil town.

'The Apaches were tasked with precision strikes against a regime radar installation and a military checkpoint, both located around Brega,' said Major General Nick Pope, the Chief of the Defence Staff's Strategic Communications Officer.

'In the same area, Royal Air Force ground attack aircraft destroyed another military installation, whilst a separate RAF mission successfully attacked two ammunition bunkers at the large Waddan depot in central Libya.'-Reuters