A Chinese researcher for The New York Times (search) has been arrested on suspicion of providing state secrets to foreigners, but authorities haven't explained what he is accused of doing, his defense lawyer said Thursday.

Prosecutors issued a formal arrest order on Wednesday for Zhao Yan (search), who was already in detention since Sept. 17, said lawyer Mo Shaoping. Mo said that technically it isn't a decision to prosecute him. But once a suspect is formally arrested in China, it is almost unheard of for the case not to go to trial.

A friend said earlier that Zhao was believed to be under investigation as the possible source of a Sept. 7 report by the Times about the planned retirement of former President Jiang Zemin (search) from his post as head of China's military. Jiang later handed over that post to his successor, President Hu Jintao (search).

The secretive Communist Party releases few details of its decision-making process and treats leaks as a serious offense.

The Times heard about the arrest order from Zhao's family, said its foreign editor, Susan Chira. But she said Chinese authorities haven't communicated with the newspaper since he was detained.

Zhao's arrest comes days before Secretary of State Colin Powell is to arrive in Beijing on Sunday for an official visit.

The Times has asked State Department officials to "express their concern" but doesn't know whether Powell might raise the issue, Chira said by phone from New York.

"We want to reiterate that to our knowledge, Zhao Yan has not been involved in any way in disseminating state secrets. We are deeply, deeply concerned," she said. "We are doing everything we can to help him rebut these charges."

The State Department earlier expressed concern over the implications for foreign reporters in China. China's Foreign Ministry responded by warning that "outside forces should not interfere" in the case.

Mo said his requests to see Zhao have been rejected, and his family is legally barred from seeing him until the case is resolved.

Notice of Zhao's arrest was issued by prosecutors in a brief document that didn't explain what he was accused of doing, Mo said.

"It's impossible to expect them to do so," Mo said. "They won't even let a lawyer meet him, so they won't tell what he is accused of doing."

Chinese law gives authorities two more months to finish their investigation, but they can ask a court to postpone that deadline for as much as seven months, Mo said.

Zhao, a former reporter for a Chinese magazine, went to work for the Beijing bureau of The Times in May.

The Times has stressed that Zhao did not report or write on his own for the newspaper and says he didn't bring it the story of Jiang's retirement plans.

Most foreign news bureaus in China employ Chinese assistants who read newspapers, monitor Web sites and help to gather information. But they are barred from acting as reporters.

Zhao's detention came amid a series of steps by Communist leaders that appear to be aimed at tightening control over public discussion of government matters.

A Chinese magazine was forced to suspend publication after it carried an article in August criticizing North Korea, a Beijing ally. In September, a popular Web site that carried discussions of social issues and foreign affairs was shut down.

Others have suggested that Zhao's detention might be related to his earlier work as a journalist before going to work for The Times.

As a magazine reporter, Zhao was known for exposing official abuses against farmers. He was also a political activist and spent three years in prison after taking part in a failed attempt to create a new political party, according to China Labor Watch, the group that first reported his detention.