The United States is seeking information from Iran about an American citizen believed to have gone missing several weeks ago in Iran, the State Department said on Monday.

The State Department had sent an official inquiry to Iran via Swiss diplomats, who play a role of a go-between with Iran as Washington has no diplomatic ties with Tehran.

"It's a private American private citizen who is in Iran on private business about whom we are pursuing welfare and whereabouts (information)," State Department spokesman Sean McCormack told reporters.

"Today, we are sending to the Iranian government through the Swiss channel an inquiry as to whether or not they have any information on his welfare and whereabouts," McCormack said.

He declined to provide more details, including the name, age or occupation of the missing man.

In addition, the spokesman also dismissed speculation that the missing American was in any way related to the current crisis between Iran and Britain over 15 sailors and marines seized last month by Iranian forces.

"We have been monitoring this situation for a couple of weeks now," he said.