A second night of attacks against targets in Afghanistan began this evening.

Senior US defence sources confirmed the renewed action as British journalist Yvonne Ridley, who was arrested by Taliban forces on September 28, was reported to have been released and crossed the border into neighbouring Pakistan.

There was no immediate confirmation of British involvement in another night of air strikes.

But earlier Secretary Geoff Hoon said that the first night of US and British air and missile strikes against Afghanistan marked only the start of a "relentless, deliberate and sustained campaign" to "root out" terrorism.

And the Chief of Defence Staff Admiral Sir Michael Boyce warned that they were in for the "long haul" with air strikes expected to continue for several more days to come.

"We know that the defeat of international terrorism is not going to be easy and it is not going to be brief," he told a news conference at the Ministry of Defence in London.

Mr Hoon confirmed that plans were being drawn up to follow up the attacks by sending in ground forces - including British troops - but he said that they may not be possible to carry out.

"It is perfectly possible that the impact of these initial strikes and those that follow will have such a seriously disabling impact on the Taliban regime that the use of ground troops may not be possible in a hostile environment," he said.

He acknowledged however that the action may destabilise the Taliban regime to the extent that the rebel Northern Alliance was able to seize the capital and take control of Kabul.

"I think that is one of the possible outcomes that may follow from military action and the removal of the Taliban regime," he said.

His comments are likely to cause alarm in Pakistan which is deeply hostile to the Northern Alliance.

The Pakistan President, General Pervez Musharraf, already facing a wave of anti-American demonstrations across the country, warned today that the Northern Alliance must not be allowed to exploit the military strikes for their own ends.

But in London, Ahmad Wali Masoud, brother of murdered Alliance leader Ahmad Shah Masoud, said its ground troops were co-operating with US and British air forces.

And he called on the coalition to supply them with financial and military aid for their fight against the Taliban.

In all, 30 sites around the country - including Afghan air defences, airfields and garrisons - were targeted in three waves of attacks by missiles and American warplanes.

Royal Navy nuclear-powered submarines launched Tomahawk Cruise missiles at a large training camp belonging to Osama bin Laden's al Qaida network at an undisclosed location.

Mr Hoon said that only three of the targets attacked had been in Kabul and four around other built-up areas and that the remaining 23 had been in remote parts of the country.

Despite claims from the Taliban that there had been civilian casualties - with reports of 20 dead - Mr Hoon insisted that strenuous efforts had been made to avoid civilian targets.

With air strikes expected for several more days to come, Mr Hoon said that British reconnaissance aircraft and air tankers would support the US operations.

However, he played down suggestions that RAF Tornado GR4 ground attack aircraft in the region would be involved directly in missions against Afghanistan.

He robustly defended the decision to go ahead which he described as an act of "legitimate self-defence" by both Britain and America.

"The Taliban regime had every chance to avoid what happened last night," he said

"We warned them they were running out of time. They were warned that they faced powerful military action. They didn't believe us, they prevaricated. Enough was enough," he said.

Downing Street announced that Prime Minister Tony Blair had now set up a formal War Cabinet which will start meeting "regularly" from tomorrow.

As well as Mr Hoon and Admiral Boyce, it also includes Deputy Prime Minister John Prescott, Foreign Secretary Jack Straw, Chancellor Gordon Brown, Home Secretary David Blunkett, International Development Secretary Clare Short and Commons Leader Robin Cook.

Mr Blair was also recording an interview for the Al Jazeera, a Qatar-based TV satellite station, to reinforce his message that the coalition's attack are against terrorists and those who harbour them and not Islam.

That is the same TV station which regularly broadcasts interviews and messages from bin Laden.

He was then meeting a multi-faith group of religious leaders, including the Archbishop of Canterbury, the Chief Rabbi and Moslem leaders, before chairing a Cabinet meeting and making a statement to the recalled House of Commons.

The Taliban, who held their own emergency Cabinet meeting, insisted however that both bin Laden and the Taliban's spiritual leader Mullah Mohammed Omar had survived last night's onslaught.

In Pakistan there were widespread demonstrations against the action, with one person reported killed and 26 injured during violent clashes between police an protesters in the city of Quetta.

General Musharraf said that he hoped that the military action would be short as he sought to calm the anger.

"I also hope that this operation should not be perceived as a war against Afghanistan or the people of Afghanistan," he said.

"It's an action against terrorists, terrorism and their sanctuaries and their supporters."

The US deployed B1 and B52 bombers based on the Indian Ocean Island of Diego Garcia and B2 "Stealth" bombers from their base in Missouri as well as carrier-borne warplanes with ships in the Gulf.

Sites in and around the capital Kabul, Jalalabad in the north and the Taliban's spiritual home Kandahar in the south were believed to have been struck at least twice.

Huge explosions were also reported near an airport close to Herat in the west of Afghanistan and the Taliban were said to be involved in widespread battles with Northern Alliance opposition forces.