Eight American activists jailed by the Chinese for protesting during the Olympics said today after being sent home from Beijing that they were interrogated for hours, deprived of sleep, and accused of having ties to the American government.

The activists were sent home late yesterday during the closing ceremony. Some were activists and artists who demonstrated against China’s occupation of Tibet; others were bloggers who photographed the protests.

Speaking outside City Hall in New York, the detainees said they were kept in cells and were allowed to leave only for interrogations, which sometimes lasted for hours. Some said they emerged more dedicated than ever to their cause.

“Our conditions were uncomfortable, but because we’re Westerners, we suffered absolutely nothing compared to what the Tibetan people suffer,” a 30-year-old musician who lives in New York, John Watterberg, said.

The American government expressed disappointment yesterday that the Olympics did not bring more “openness and tolerance” in China.

China’s Foreign Ministry said in a statement today that “the protesters participated in ‘Tibet independence’ activities and that is against China’s law.”

The statement said China hoped “the relevant countries will teach their citizens to abide and respect China’s laws.”

Mr. Watterberg and another New Yorker, Jeremy Wells, said they were tackled and detained the evening of August 20 while staging a demonstration with two other activists outside the National Stadium, one of the main Olympics venues.

During an initial interrogation, they were told they had broken Chinese law and would be held for 10 days. They were then moved to a detention center, where they were locked in a cell and allowed to leave for interrogations that lasted between four and 16 hours.

With lights shining on them, prisoners were locked into high-backed metal chairs with bars across their laps.

Interrogators, sometimes speaking through interpreters, would not let them sleep and accused them at times of working for state-funded groups and organizations that had ties to the American government, the activists said.

“They asked about our actions, our roles, about our lives — everything from where I went to high school to everything I ate in China,” Mr. Wells said.

Detainees said they wore dirty uniforms of red T-shirts and black shorts. Drinking water was turned on for only 15 minutes a day, so prisoners would scramble to fill old soda bottles or other containers.

“It was the scariest — it was beyond anything I could imagine in a movie,” a 28-year-old photojournalist from New York, Jeff Rae, said. Mr. Rae said he was videotaping a demonstration when he was detained August 18.

Some of the detainees said they asked daily to speak with the American Embassy but were not allowed to do so until a day or two after they were imprisoned.

They said they were given no warning about their release and were not told why they were being let go. Once the prisoners were rounded up and put into vans, possessions that had been seized days earlier were returned to them. The luggage the detainees had left at their hotel rooms was also rounded up and given back.

Many detainees said the Chinese officials kept some of their electronics, like cameras, laptops, and media cards.