With 50 days to go until the start of the Olympics, an anti-terrorist force of almost 100,000 commandos, police and army troops has been put on high alert, an official said yesterday.

"Terrorist attacks may occur before the Games, so our anti-terrorist forces have been in action ahead of the opening ceremony," Liu Shaowu, director of BOCOG's security department, said.

The end of a series of anti-terrorist drills entitled "Great Wall 5" staged earlier this month marked the beginning of the campaign, he said.