U.S. officials are expressing skepticism about Iran's disavowal of knowledge about a retired agent of the U.S. Federal Bureau of Investigation believed missing in Iran for more than a month. The United States and Iran have had a rare diplomatic exchange on the case, via their Swiss intermediary. VOA's David Gollust reports from the State Department.

The State Department says it has asked two unnamed European countries to intercede with Iran in the disappearance case, after receipt of what officials suggest was a disappointing Iranian response to U.S. diplomatic inquiries on the matter.

The case involves a 59-year-old retired FBI agent, Robert Levinson, who the State Department says was last seen in early March on Iran's Kish island, a Persian Gulf beach resort that Americans can visit without a visa.

The State Department had made several inquiries about Levinson to Iran, relayed by the Swiss government, which looks after U.S. interests in Iran in the absence of diplomatic relations between Washington and Tehran.

In a talk with reporters, State Department Spokesman Sean McCormack said a terse Iranian reply arrived late Wednesday via the Swiss embassy in Washington, and that Iran denies any knowledge of Levinson even though U.S. officials believe he is still there.

"Yesterday in the afternoon, we received a response from the Iranians saying they didn't have any record of Mr. Levinson, concerning his whereabouts," said Sean McCormack. "That, shall we say, is a response that we will continue to pursue with the Iranian government, because we have assured ourselves to a great degree that Mr. Levinson is in Iran."

A senior official who spoke to reporters here said U.S. officials looking into the case were able to determine that Levinson arrived at the Iranian island last month and checked into a hotel there.

He said it "strains credibility" that Iran has no information about his whereabouts, and that the State Department is skeptical about the Iranian reply.

He said the United States hopes that the European governments being asked to intercede in the case, which do have formal relations with Iran, will be more successful in getting information.

The State Department has said Levinson, who left the FBI several years ago, was not on any mission for the U.S. government. News reports have said he was in Iran doing research for an independent film-maker.

There have been several media reports suggesting that Levinson is in custody in Iran, and that he may be held as a bargaining chip for the release of five Iranians held by U.S.-led forces in Iraq.

However, spokesman McCormack said the United States is making no allegations to that effect, and that reports that Levinson has been detained are just speculation.