China has detained a researcher working for the New York Times on suspicion that he helped break news that aging leader Jiang Zemin planned to retire from politics this month, sources familiar with the case said Thursday.

Zhao Yan, a former reporter for the magazine China Reform, was arrested by state security agents on Sept. 17. Jiang stepped down from his post as head of the military on Sept. 19, during the annual meeting of the ruling Communist Party's Central Committee.

Earlier this month, the newspaper quoted sources as saying Jiang would hand the chairmanship of the Central Military Commission to Hu Jintao, his successor as president and party chief, at the plenum, completing a leadership transition that began at a party congress in 2002.

Zhao was taken into custody on suspicion of illegally providing state secrets to foreigners, according to a copy of an arrest document issued by the Beijing state security bureau and dated Sept. 21.

State security "suspect him to be the source of the Jiang Zemin story," said a source speaking on condition of anonymity. Zhao has worked for the New York Times since May.

The Times's foreign editor, Susan Chira, denied the charges and said the paper was "deeply concerned" about the case.