BEIJING — China has stationed a battery of ground-to-air missiles just 300 meters (yards) from a Beijing Olympic venue, another sign of the tightening security with the games less than seven weeks away.

The fenced-off military compound has been set up just south of the Olympic Sports Center Stadium, a venue for soccer and modern pentathlon. It's also within a kilometer (half mile) of the Water Cube and the Bird's Nest National Stadium, the US$450 million showpiece venue of the games.

At least two Hongqi 7 missile launchers were visible behind a two-meter-high (7-foot) fence, with military hardware and vehicles hidden under camouflage netting. Dozen of soldiers guarded the compound on Tuesday with a notice posted on the fence: "Military Administrative District No Admittance."

The Beijing Olympics are intended to showcase the country's rising political and economic power. But the intense media scrutiny is also giving environmentalists and political activists with grievances a potential stage for protest, which could lead to a public-relations disaster for the image-conscience communist government.

The Athens Olympics four years ago were also under tight security with Patriot anti-aircraft missiles stationed around the city. Those games came just three years after the terrorist attacks on the United States.

China has clamped down in every phase of security since deadly rioting in Tibet broke out on March 14, followed by pro-Tibet protests on international legs of the torch relay.

On at least three occasions this year, authorities say they foiled plots by separatists from Xinjiang — the far western, Muslim-dominated region of China — that targeted the Olympics. The plots included alleged attempts to crash an airliner and kidnap athletes and journalists.

Little evidence has been provided, however, and many foreign security experts question the scale of the threat while rights groups say Beijing may be using terrorism as cover for crackdowns on legitimate peaceful dissent.

Last week Beijing said it had mobilized a 100,000-strong anti-terrorism force to guard against threats to the Olympics. Police commandos, specialist units and regular army troops made up the force. It also included the paramilitary Snow Wolf Commando Unit, which will handle terrorist alerts and public unrest during the Aug. 8-24 games.

China has toughened visa rules ahead of the games, targeting students and business officials who travel frequently to the country. This has been coupled with frequent sweeps of areas where foreigners live, with police checking documents and residence permits.

TV broadcasters are also saying they may be hindered from moving freely around the city and reporting the games, a promise Beijing made when it was awarded the games seven years ago.