By Steve Kingston BBC correspondent in Washington

Having raised the threat level to high, the Bush administration has issued some guidance for the American people as to what to do in the event of a nuclear, biological or chemical attack.

Entitled Are You Ready? the White House guidance runs to 15 pages, offering advice on how to deal with everything from an explosion in a building to an all out nuclear attack, although reassuringly it says the threat of the latter has receded since the end of the Cold War.

The document lists the obvious prime targets for terror attacks: airports, power plants, major landmarks and financial centres.

But it also says hotels and apartment blocks could be vulnerable, which is why families are being urged to keep emergency food and first aid supplies and to learn where the emergency exits are located in their buildings.

'Dirty bomb'

Beyond that, the government recommends its citizens buy battery-operated radios and perhaps even hard hats.

There is a reminder too of the now familiar procedures for dealing with an anthrax attack and hints on decontamination after a chemical alert.

As for a nuclear attack, the government says this would most likely come in the form of the so-called dirty bomb, combining conventional explosives with crude radioactive material.

Such a device, it says, could be delivered in a suitcase.

Finally, if America were to come under full-scale nuclear attack, the official advice is do not look directly at the fireball, then take cover under ground to avoid radioactive fallout.