BEIJING - Beijing police have detained the organizer of a planned 5,000-strong memorial march to mourn China's deposed Communist Party chief Zhao Ziyang, the organizer's wife and sources said on Sunday.

The security apparatus, obsessed with stability, have been on alert against any protest in the wake of Zhao's death on Monday. Zhao was toppled as party chief in 1989 for opposing the army crackdown on the Tiananmen Square student-led demonstrations for democracy and lived under house arrest for more than 15 years.

Zhao Xin, 36, a student who negotiated with the government in 1989 and is now an executive at a Beijing real estate company, was taken into custody on Friday after police rejected his protest application, his wife Bi Ning said. The two Zhaos are not related.

"Police came to our home and took him away. He took with him some books and a change of clothes," Bi told Reuters.

"I phoned the police who told me not to worry and said he's fine. But I feel uneasy because I'm in the dark about his situation," the wife said.

Zhao Xin was held without trial for one year for his role in the Tiananmen protests.

Two sources close to Zhao said he had applied to police for permission to stage the march to Zhao's home in central Beijing from Tsinghua University in the western part of the capital.

Police rejected the application on grounds that it should have been submitted seven days beforehand.

Zhao had planned to stage the protest on Sunday.

"It's preposterous. It's unreasonable," one of the sources, who spoke on condition of anonymity, said of police turning down the application.