BEIJING - A former student leader of China's 1989 pro-democracy movement has been arrested on fraud charges, his family said on Wednesday, weeks before the 20th anniversary of the June 4 crackdown on Tiananmen Square protests.

The arrest of Zhou Yongjun, a leader of the Beijing Students' Autonomous Union in the 1989 protests, comes after months in secret detention following his return from the United States.

Zhou is a permanent U.S. resident, relatives said, and his case could stoke contention between Washington and Beijing.

He was charged with fraud by police in his home city of Suining in southwest Sichuan province, said his brother, Zhou Lin, who spoke by telephone. Zhou Lin said his family received the written arrest notice on Wednesday morning.

Zhou Lin said he did not know the specifics behind the accusation, nor when his brother could have committed fraud in China, given his long residence in the United States.

Zhou Yongjun's partner, Zhang Yuewei, called the charge unfounded.

He's been under secret detention for a long time, since he tried to enter China last year, said Zhang, speaking from California, where the couple live.

At first he was accused of spying and political crimes, but now they have switched to this financial fraud accusation.

Calls to the Suining Public Security Bureau either went unanswered or officers said they did not know of the case. The U.S. Embassy in Beijing had no immediate comment.

Zhou, 41, was a law student who helped organize the mass movement demanding democratic reform that erupted on Chinese streets in 1989. He was on Tiananmen Square on June 4 that year as armed troops moved in to quash the protests, according to accounts from the time. Hundreds died in the crackdown.

After years in detention, Zhou fled to the United States in 1993. When he tried to return to China in 1998, he was sentenced to three years of reeducation through labor and returned to the United States in 2002.

When he again tried to enter mainland China in September last year, he was detained when he tried to cross over from Hong Kong said his family. He recently moved to Suining.

He wanted to see his father, who is old and sick, but I didn't want him to go, said Zhang.

China California