In pictures: Army patrols Heathrow

More than 400 soldiers and armoured vehicles have joined police at Heathrow Airport to boost security amid concern over al-Qaeda attacks.

Police fear the Muslim religious festival of Eid this week may trigger an attack on the capital

The troops will continue to be deployed at the airport as long as they are needed

Security was bolstered following intelligence reports, said Metropolitan Police commissioner Sir John Stevens

The heightened security is a precautionary measure and the public should not panic, said police

But scenes like these at the airport are unprecedented, said BBC home affairs correspondent Daniel Sandford

The Home Office warned last November of the possibility of "devastating" terror attacks

The operation at Heathrow is the most visible sign of security being stepped up in the capital