(Adds that inquiry been delivered to Swiss)

By Sue Pleming

WASHINGTON, April 2 (Reuters) - The United States asked Iran on Monday to provide information about a former FBI agent believed to have gone missing several weeks ago while on private business there, U.S. officials said.

State Department spokesman Sean McCormack said the family and employer of the man reported him missing and the State Department sent an official inquiry on Monday to Iran via Swiss diplomats, who act as a go-between with Tehran because the two countries do not have diplomatic relations.

"His family and his employer are seeking to determine exactly where he is," McCormack said, declining for privacy reasons to provide any details on the man or his employer.

A State Department official said later it would probably be several days before Iran's government acknowledged the inquiry passed on by the Swiss Embassy in Tehran.

The FBI confirmed the missing man had worked for the FBI more than a decade ago but said he was not in Iran on any official business and his work at the agency had not focused on Iran.

"The individual is not an FBI contractor. Furthermore, the individual's primary assignments in the FBI focused on criminal matters, such as traditional organized crime," the FBI said in a statement.

"At this time, there are no indications that this matter should be viewed other than as a missing person case," the FBI added.

McCormack also emphasized the American was in Iran on private business and was not working for the U.S. government.

"We don't see any linkage between this case and any ongoing cases in the news recently," McCormack said, referring to 15 British sailors and Marines who are being held captive by Iran, which says their vessel strayed into Iranian waters.

Relations are very tense between the United States and Iran, particularly over its nuclear program. The two nations have not had diplomatic ties for nearly 30 years.

The missing man, described by officials as middle-aged, is believed to have been visiting Kish, an Iranian resort island and free-trade zone in the Gulf. He is not believed to be of Iranian descent and his wife lives in the United States.

McCormack said the United States had been monitoring the situation for several weeks but had not so far found any information on the man's whereabouts.

A State Department official who spoke on condition of anonymity, said the department learned of the case about March 11 and had not so far uncovered any reliable information to indicate the Iranian government was involved.

Secretary of State Condoleezza Rice had been briefed about the case, he said, without providing further details. He added that there were two to three cases every year of Americans who were reported missing in Iran.

"It's not completely a unique scenario to have an American citizen go missing there and possibly need consular support," White House spokeswoman Dana Perino said.

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