Iran said it did not have any information about a former FBI agent who reportedly went missing in the country nine months ago, comments likely to disappoint the American's visiting family members.

The wife and son of Robert Levinson say he disappeared in March after he travelled to Iran's Gulf resort island of Kish to investigate cigarette smuggling for a client. They arrived in the Islamic Republic on Tuesday to search for him.

Accompanied by Swiss diplomats, who represent U.S. interests in Tehran because the two old foes have not had diplomatic ties since shortly after Iran's 1979 Islamic revolution, Christine and Daniel Levinson met Iranian officials and also went to Kish.

But government spokesman Gholamhossein Elham suggested they had not been able to find out more about his fate.

"We have no information about him and at the same time no information confirming his disappearance. But we welcome any information which can help us in this matter," Elham told a news conference when asked about their four-day visit.

"We told them to provide us with any useful information to help us follow up this case and settle this issue," he said.

Levinson retired from the FBI's New York office a decade ago and had taken a trip from Dubai to Kish to investigate< counterfeiting and smuggling of cigarettes for a client, likely a tobacco company, his wife has said.

U.S. officials have said they believe Levinson is in Iran but they have no credible information on his whereabouts. The Iranian government has said it investigated the case but did not know what happened to him.

Levinson called his wife on March 8 before boarding a plane from Dubai to Kish. He told her he had left most of his luggage at a Dubai hotel and would be back within 24 hours, but he failed to call on March 10, his 59th birthday.