LONDON, March 16: Undercover guards will accompany British and American athletes at the Athens Olympics in August as part of unprecedented anti-terrorism measures, it was reported Tuesday.

But Greece, which will deploy more than 40,000 security staff during the Games, has ruled out foreign guards being armed. The London Evening Standard reported on Tuesday that British and American plainclothes officers plan to watch competitors when they leave secure zones like the athletes village and sporting venues and go into public areas.

Following the Sept 11 attacks on the United States in 2001, the Iraq War and last week's Madrid train massacre, the Athens Games will be the most heavily-guarded event in the 108-year history of the Olympics.

While security at the 2000 Sydney Games was largely a police responsibility, the Athens Olympics will be dominated by a military operation which is costing 650 million euros (820 million dollars), three times as much as four years ago.

International Olympic Committee President Jacques Rogge said at the weekend the Madrid bombings had triggered another security review. And last Greece asked NATO to provide aerial and sea surveillance against a chemical or nuclear attack.

An international security exercise against terrorism has just started in Greece, involving 1,500 police and an overseas force of 400 American soldiers and 100 from Britain, Germany, Israel and Canada.

Scotland Yard's David Vennes, Britain's top anti-terrorism official, has travelled to Athens to observe the "Shield of Hercules" exercise. It is understood that countries regarded as high risk - such as the United States, Britain and Israel - will be allowed to bring their own experts. Armed Greek guards will also be placed on team buses on their way to and from stadia. -AFP