YINING, China — Security forces squeezed their grip on China a notch tighter today for the start of the Olympics, edging up restrictions in the capital and imposing much tougher ones in a restive Muslim area in the country's far west.

The Beijing Games' glittering curtain raiser went off without any obvious signs of trouble, a day after an Islamic group seeking independence for Xinjiang province threatened to attack buses, trains and planes during the two-week competition.

In Beijing, authorities closed streets and iconic Tiananmen Square for most of the day as President Hu Jintao hosted dozens of world leaders at a luncheon in the adjacent Great Hall of the People. Motorcades later sped the dignitaries, including President Bush, to the main Olympic stadium for the evening ceremony.

The square reopened, and thousands flooded in to watch a fireworks show after the ceremony, hemmed into designated areas by armed police. Hundreds of celebrating Chinese who gathered outside the stadium, known as the Bird's Nest, were also ringed by police.

Normally bustling streets in the capital fell unusually quiet after city officials asked people to keep to organized sites with giant television screens or stay home to watch the ceremony.

A 100,000-strong contingent of police and special forces are safeguarding Olympics venues, while hundreds of thousands of Beijing residents have been formed into voluntary security patrols.

The mood was tenser on the other side of the country, near China's border with Pakistan and Afghanistan, where anti-terrorism police patrolled towns in Xinjiang province and authorities shut down a bustling bazaar in the region's main city for security reasons.

Xinjiang, home to the Muslim Uighur minority that has long had difficult relations with the central government, has been on edge since a brazen attack Monday by two men who used a truck, bombs and knives to kill 16 border policemen and wounded another 16.

On Thursday, a videotape purportedly made by the Turkistan Islamic Party, a militant group seeking independence for Xinjiang, was released with threats of attacks during the Olympics. The group is believed to be based across the border in Pakistan, where security experts say core members have received training from al-Qaida.

Here in Yining, the site of a major protest in 1997 by Uigars demanding Xinjiang independence, streets were eerily empty and most shops were closed during the opening ceremony. The few people on the sidewalks were youths and adult men wearing red arm bands that said "safety inspection personnel." Some held black rubber riot clubs.

Occasionally, the sirens of a convoy of police SUVs and armored troop carriers could be heard driving around the city in an anti-terrorist drill. Residents said the maneuvers had been going on daily since Monday's deadly attack in Kashgar, a city 620 miles to the south.

An Associated Press reporter was picked up by police while speaking with people watching the Olympics ceremony on a TV set up in the street. The reporter was taken to a police station, videotaped and kept for 45 minutes while his passport, press card and cell phone were taken away and inspected.

An AP photographer was also briefly held by police who forced him to delete pictures of the police convoy doing maneuvers on the street.

Such detentions happen to foreign reporters from time to time in China, though Beijing has promised international media will be able to report on the Olympics freely.

In Xinjiang's provincial capital, Urumqi, a sign at the entrance of the International Bazaar said the area, surrounded by mosques with minarets, was off limits.

One of the many security guards in the bazaar's plaza, which was marked off with crime scene tape, told the AP: "The area is closed because of a possible terrorist attack. It's just a defensive measure." He refused to give his name.

Security guards checked bags at the entrances of hotels, department stores and discos in the busy city.

Xinjiang is a mineral-rich expanse that covers a sixth of China's land mass and borders eight Central Asian nations. It is populated by Uighurs, a Turkic Muslim ethnic group, in which many people favor independence or greater autonomy for their region.

At a shopping plaza in Urumqi, one Uighur businessman who would only identify himself as Kurban, said he did not support violent groups and valued his relationship with Han Chinese, the ethnic majority. But he also sympathized with Uighurs who are forced to live in poverty and repression in the countryside.

"The countryside is tense and very poor," he said. "But if I talk about them anymore, the police will come and take me away."

Associated Press writers Henry Sanderson and Cara Anna in Beijing contributed to this report.