Britain deployed troops at Heathrow Airport in an effort to boost security because of a potential terrorist threat to London, police said Tuesday.

The Metropolitan Police said it was possible the Al Qaeda terror network would use the end of the Muslim Eid al-Adha holiday to mount attacks. The religious festival runs from Wednesday to Saturday this week.

"From time to time, it is necessary to raise levels of security activity. We think it is prudent to do so now," police said in a statement.

Britain is Washington's main ally in its standoff with Iraq and the security warning here comes after the Bush administration on Friday raised the national terror alert from yellow to orange.

Police said the heightened security in Britain's busiest airport would involve use of military personnel to support officers. The statement did not say how many soldiers would be deployed.

A police spokesman said that normally the army is not used to police Heathrow Airport, west of London. He also said the measures came into effect Tuesday morning.

"The strengthened security, which is likely to be most visible to the public at Heathrow Airport, relates to a potential threat to the capital," the statement said.

Police said the measures were related to precautions being taken in other countries, without naming them.

The statement said the measures were being taken because of "the possibility that the end of the religious festival of Eid may erroneously be used by Al Qaeda and associated networks to mount attacks."

No further details of the nature of the threat or the new security measures were immediately available.

Last November, a statement authorized by Home Secretary David Blunkett warned of "ever more dramatic and devastating" terror attacks, but avoided mention of the specific threats.

"If Al Qaeda could mount an attack upon key economic targets, or upon our transport infrastructure, they would," the Home Office statement said.

Earlier, the Home Office had issued -- and then hurriedly withdrawn -- a statement warning that Al Qaeda might be prepared to use a radiological device known as a "dirty bomb," or some kind of poison gas. It was replaced with a more general warning of terrorist threats.

Police in Britain have conducted arrested a series of terror suspects since the Jan. 5 discovery of the deadly poison ricin in a north London apartment.

In raising the U.S. terror level, Attorney General John Ashcroft cited an "increased likelihood" that the Al Qaeda terror network would attack Americans, noting hotels and apartment buildings were possible targets.

Police in the United States last week stepped up security at airports, subways and hotels after the country was put on a heightened terror alert.