Police later admitted there were serious doubts about whether the suspects were terrorists. But a huge security blanket has been thrown over the Thai capital to protect athletes and dignitaries ahead of Sunday's official opening by King Bhumibol Adulyadej. And police narrowly averted a riot at a rehearsal for the opening ceremony.

More than 16,000 security forces have been drafted in for Thailand's biggest peace-time security operation to guard what organisers are billing as ``the last great sports festival of the 20th century.'' Demonstrations have been banned and a special US-trained force to handle kidnapping and terror attacks has been put on duty for the Games which run from December 6 to December 20.

There was no visible tightening of the measures, however, following the detention of the four suspects, who police atfirst alleged were carrying bomb making equipment. The Pakistan embassy later accused police of framing the suspects and beating them to get confessions.

Prime Minister Chuan Leekpai moved to soothe terrorism fears, saying police and the military had the situation under control.

``It is our duty to take care of security as best as we can. There is nothing to be concerned about, but we do not want to be careless,'' Chuan told reporters.

Major General Banchorn Chavansil, responsible for anti-terrorism measures at the Thai military Supreme Command, added: ``The military is confident that it can control the situation regarding action targeted against the Games or foreign embassies, or anything.''

But police were confronted by angry scenes during a dress rehearsal for the opening ceremony on Tuesday night.

Thousands of angry spectators threatened to burn cars if they were not let in to what was meant to be a closed event. Officials ordered the gates of the Rajamangala National Stadium opened when policesaid they could not cope.

The announcement of the arrests also came as workmen and troops raced to finish some facilities for the Games.

There have already been complaints about some stadiums, with widespread repairs ordered on one pitch following a public condemnation by Asian Football Confederation general secretary Peter Velappan.

There were also reports of Hong Kong footballers being overcome by fumes before their 6-0 defeat to Oman on Monday. Sources said their dressing room was only painted two hours before the match and several players were taken sick. Two new toll roads were opened in a move to significantly reduce the risk