Nato may be making contingency plans for a potential terrorist attack

There are concerns the first summer games since the 11 September 2001 attacks against the US could be targeted by terrorist groups.

In what would be an unprecedented role for the alliance, Nato may provide surveillance planes and make plans to provide relief in case of attack.

Greece may delay a formal request until after parliamentary elections in March.

The Greek constitution stipulates that the government must seek approval from parliament before allowing uniformed foreign troops into the country.

"Nato can assist, Nato will assist, Nato is in a position to assist," Jaap de Hoop Scheffer said on Thursday after talks with Greek Foreign Minister Tassos Giannitsis.

Unprecedented security

The Athens Olympics, which begin in six months' time, will be the first summer games to be held since the 11 September attacks on the US.

The Greek authorities are leaving nothing to chance and are preparing the biggest security operation in the history of the Olympics.

This is no longer a Greek security operation, but an international one Athens Mayor Dora Bakoyanni

More than 50,000 members of the security forces and emergency services will be directly involved in protecting the athletes, officials and visitors.

On Thursday a state legal board approved government plans to deploy thousands more Greek troops to provide a protection and patrol unit, AP news agency reported.

The total cost for Greece could be more than $1bn.

International security operation

"What is extremely important is that we don't feel alone," Mayor Dora Bakoyanni of Athens said.

"This is no longer a Greek security operation, but an international one."

A specially formed Olympics advisory group of seven countries - Australia, Britain, France, Germany, Spain, Israel and the US - meets monthly to provide advice about security measures.

Britain, which leads the group, designed this month's exercise for the Greek security forces and emergency services - one of the biggest anti-terrorist exercises ever held in Europe.

The aim was to test the ability of around 2,000 members of the Greek police, military, coast guard, fire brigade and medical services to react to an attack involving a weapon of mass destruction.