WASHINGTON (AFP) - A former aide to US Secretary of State Colin Powell has been arrested after he allegedly concealed a trip to Taiwan and passed documents to the island's intelligence agents, court records showed.

Donald Keyser, who retired in July as principal deputy assistant secretary for East Asian and Pacific Affairs, was followed September 4 by Federal Bureau of Investigation agents to a Washington restaurant where he was seen handing over some documents to two Taiwanese agents, according to the records.

The documents were described by an FBI affidavit filed in US District Court in Alexandria, Virginia Wednesday as something "derived from material to which Keyser had access as a result of his employment with the Department of State."

He told FBI agents the documents contained "talking points" that he often would prepare for his meetings with the Taiwanese.

Keyser was not charged with spying in the court papers but with violating State Department rules by failing to disclose a side trip he took to Taiwan last year during a visit to China and Japan.

Keyser, who advised Powell on China issues, met one of the Taiwanese agents in Taipei in September 2003, the court papers said.

Keyser sent his retirement papers in July but is technically still a State Department employee and currently assigned to the Foreign Service Institute, which runs a career transition process for retirees.

In 2000, he made the news over a missing top-secret laptop computer in the State Department.

As one of six State Department employees blamed for lax security at the department, he was suspended for 30 days and reassigned by then secretary of state Madeleine Albright.

"I would say that we are cooperating and have been cooperating with the investigation," department spokesman Richard Boucher told reporters.

He said Powell had been "fully aware of this matter" for months.

Keyser was released after posting a bail of 500,000 dollars pending a court hearing of his case on October 13, a spokeswoman for the Attorney General's office told AFP.

The United States does not have official diplomatic links with Taiwan and it is rare for diplomats to travel to Taipei, especially in any official capacity, without specific permission.

The United States shifted its diplomatic recognition from Taipei to Beijing in 1979 and acknowledges Beijing's position that Taiwan is part of China.

When questioned about his travel to Taiwan, Keyser said he had taken annual leave while on official travel to Japan and had flown to Taipei for sight-seeing purposes, FBI special agent David Farrell said in his affidavit.

The arrest of Keyser, one of the nation's leading experts on China, has surprised those in diplomatic circles. It is the second case in recent months of a federal official being implicated in passing documents to US-friendly states.

A Pentagon policy analyst was last month alleged to have provided a draft presidential directive on Iran to an American-Israel group amid fears that the information could have landed in Israel.

"There is no question that Don is one of the brightest, one of the most capable foreign service officers in the state department," an ex-senior US diplomat said, referring to Keyser.

"But reports that he would go and brief Taiwanese intelligence officials dumbfounds me because if he wanted to make sure Taiwan got this information, he would talk to Taiwanese diplomats.

"There is no sense in talking to the spooks. It just defies understanding."