Three Americans were detained Friday after trying to protest near a key Olympic venue just an hour before the games' opening ceremony, according to a pro-Tibet group.

Three men from Students for a Free Tibet displayed Tibetan national flags near the entrance to the Beijing National Stadium, also known as the Bird's Nest, just before the ceremony began, the New York-based group said in a statement.

They were grabbed and "immediately and forcibly detained" by police, it said.

Photos posted on the group's Web site showed police officers grabbing two protesters who were waving Tibetan flags. The other man, draped in a Tibetan flag, was on the ground with two officers on top of him.

"The Chinese government wants the world to be dazzled and distracted by the grandeur of the opening ceremony, but its true face can be seen in its ruthless and intensifying repression of the Tibetan people," the group's executive director Lhadon Tethong said in the statement.

The three men were identified by the group as Americans Jonathan Stribling, 27, of Oakland, California; Kalayaian Mendoza, 29, of New York; and American-Argentine Cesar Maxit, 32, of Washington, D.C.

The Beijing Public Security Bureau could not immediately confirm the incident.

Tiananmen Square has been sealed off. Chinese authorities were on their highest alert Friday in the run up to the Olympics opening ceremony.

Beijing considers the games, in which it has invested billions of dollars, a huge source of national pride and is doing all it can to make sure it goes off without a hitch — such as ugly television images of protesters scuffling with police.

Authorities this week deported at least seven foreigners who protested at Tiananmen Square and near a major Olympic venue.

Three Americans — Rev. Patrick Mahoney, Brandi Swindell and Mike McMonagle — were sent back to Los Angeles after unfurling banner "Jesus Christ is king" in the square for two consecutive days, criticizing the government's handling of issues ranging from forced abortions to pro-democracy demonstrations in 1989.

Another group of foreign activists was also deported to San Francisco and Frankfurt, Germany, Thursday — a day after putting up "Free Tibet" banners on lamp poles outside the Beijing National Stadium.

A Chinese woman who protested the forced eviction from her house Monday at Tiananmen Square, has been put under a three-day detention, her family said.

Zhang Wei was among a group of angry residents who lost their traditional family compounds near the square to make way for the city's redevelopment.

Her son Mi Yu said Zhang called home Thursday, saying she would be officially detained for three days.

Police would not comment.

Tiananmen, at the heart of the Chinese government but also a powerful symbol of reform since a deadly crackdown on pro-democracy protesters in 1989, was locked down ahead of the games' opening ceremony Friday evening.

Trains are not stopping at the two stations near the square, and police patrolled an extensive security cordon at the square and the adjacent Great Hall of People, where President Hu Jintao hosted President Bush and dozens of other leaders at a lunch before they attended the Olympic celebrations.

In the Nepalese capital of Katmandu, hundreds of Tibetan exiles demonstrated outside the Chinese embassy Friday demanding an end to what they say is Beijing's brutal rule in the Himalayan territory.

In semi-autonomous Hong Kong, Briton Matt Pearce was detained after unfurling two banners on a major bridge. Pearce hung banners reading, "We want human rights and democracy" and "The people of China want freedom from oppression."