Tanks roll on British streets

The extraordinary security operation began after British intelligence warned of the threat of a possible missile or rocket attack on a passenger aircraft to coincide with the end of the Muslim festival of Eid al-Adha. Hundreds of troops in Scimitar light tanks were drafted in to the airport to support a police presence of 1,000 officers. Troops were also deployed on the M25 motorway, in Windsor Great Park to the west of Heathrow and around London.

With both the United States and Britain on the highest state of alert since the 11 September attacks in New York and Washington, tensions were exacerbated last night by a broadcast on the al-Jazeera television station of an audio tape said to be from Osama bin Laden, the al-Qaeda leader. Colin Powell, the US Secretary of State, was convinced it was genuine.

In the broadcast, bin Laden issued a chilling rallying call to Muslims to rise up against the US. He warned Arab states against supporting an invasion of Iraq and called on Iraqis to engage in suicide attacks.

Bin Laden said: ‘‘We stress the importance of suicide bombings against the enemy, these attacks that have scared Americans and Israelis like never before.

"We are following with great concern the preparations of the crusaders to launch war on the former capital of Muslims and to install a puppet government.

"Fight these despots. I remind you that victory comes only from God.’’

Intelligence sources have been concerned that previous broadcasts claimed to be by bin Laden have acted as a call to arms to his supporters. They have triggered several terrorist incidents, including the Bali bombing, which left almost 200 people dead last October.

Mr Powell used bin Laden’s statement to argue that it showed why the world needed to be concerned about Iraqi ties to terrorism. He said: ‘‘This nexus between terrorists and states that are developing weapons of mass destruction can no longer be looked away from and ignored."

But the deployment of armoured vehicles on British streets prompted Muslim groups to accuse the government of trying to frighten the public into supporting military action. Massoud Shadjareh, the chairman of the Islamic Human Rights Commission, said he had been deeply insulted that a terrorist alert had been linked to the Eid al-Adha festival. He said: "It is like suggesting that Christians would use Christmas to bomb Jewish, Muslim or Buddhist communities. It is unbelievable rubbish."

Downing Street insisted the decision to call in the army was based on a real threat. It confirmed the Prime Minister had taken the decision.

Last November, Mr Blair, attempting to play down fears of a gas attack on the London Underground, had promised the public would be made aware of any specific threat to Britain. However, the reasons for yesterday’s alert remained secret.

In the US, the government warned the public to prepare for a chemical, biological or nuclear attack. Officials advised stockpiling enough food, water and medicine to last at least three days, and to have tape and plastic sheeting to seal windows and doors.

Tom Ridge, the US homeland security secretary, said the alert was "the most significant" since the 2001 attacks. He added: ‘‘We believe the threat has substantially increased in the last couple of weeks.’’

A meeting of NATO ambassadors called to heal the growing rift between France, Germany and Belgium and the US and Britain was abandoned in Brussels after 20 minutes. Neither side was prepared to cede ground.

Yves Brodeur, a NATO spokesman admitted: "We do not have a conclusion."

At the UN headquarters in New York, Germany, which holds the rotating presidency of the Security Council, claimed only four of the 15 countries on the council were holding out against efforts to seek a peaceful solution for Iraq. A senior German official said the fault lines would become clear when the UN weapons inspectors present their latest report on Friday.

Last night, the Pentagon announced US planes had attacked a ballistic missile system in southern Iraq, marking the first attack on Iraqi missiles meant to attack ground targets instead of aircraft or ships at sea.

The Iraqis had moved the missile system into the southern no-fly zone, according to US officials.