An American citizen is missing in Iran, the State Department said today.

Sources tell ABC News that the missing American was a former FBI agent, although they stressed that he was now a private citizen and that his trip to Iran was on "private business" and not associated with official U.S. matters.

State spokesman Sean McCormack said that the United States had been monitoring this case for several weeks and today had sent a message to Iran through diplomatic channels for more information on his whereabouts.

State Department officials say that Iran has yet to respond with any information. Because the United States does not have diplomatic relations with Iran, the message was passed on by the Swiss Embassy in Tehran.

McCormack said the United States had been in touch with the man's family and employer, who were the first ones to report him missing. A senior State Department official tells ABC News the man was last seen in early March in Iran.

The official says that right now nobody seems to know where he is, but that the United States is asking Iran for any information because that's where he was last seen. According to one official, there is "no reliable information" that the American is being detained by Iran.

McCormack denied any connection between this case and that of the 15 British sailors and marines being held by Iran for allegedly straying into Iranian waters in the Persian Gulf.

"There is no linkage with this or any ongoing cases that may have been in the news recently," he told reporters.

Kondracke: I've got to say , Tony Blair is not exactly acting like Margaret Thatcher would act under these circumstances. He's acting like Jimmy Carter would act. It's "tip-toe" you know. one idea that I heard today was that britain might threaten to close an Iranian port and if the Iranians said, well, you don't have any ships around to do that --- oh yes, we do, we have submarines and they wouldn't know where the submarines are and close down a port and ratchet up the problem.

Hume: Does that come from someonw who knew that the Brits might do this?

Kondracke: Uhm. No.

Barnes: Hey they could use American ships. There are two carrier groups in the gulf. And I would think that the thing President Bush would have done would have been to call Tony Blair and say, "Look, these are your people and we'll back you on whatever your policy is, including a military option if that is what has to take place."

Hume: Our correspondent James Rosen is reporting that this is a series of steps, that you sort of walk through the UN to try to get this to something that might matter...

Barnes ... that's a strategy of "strong letter to follow." It's really not much.

Hume: Is it worth going to the UN at all?

Barnes: Well, you know, they're "low keying" it ...

Hume: Well, that's a first step

Barnes: I know, but the last step is some resolution sanctioning the Iranians and they're already defying another one in the nuclear...

Easton: ...the British...you've gotta be careful with this regime. This reveals a regime that wants to be considered a government. It's already been marginalized with the sanctions that the UN passed by the security counsel this Saturday. They're acting like a rogue terrorist outfit. Trotting this woman out. The letter. They're acting like a terrorist organization. They're a terrorist organization with a lot of economic power. Already we saw oil prices spike up. There's analysts saying it could go up as high as 80,90,100 dollars a barrel...

Barnes: ... the point she's making is that they're making money on this. The longer they keep it going. Look, there's one thing you could do and it doesn't mean shooting at anybody and that's we could block the ships from leaving port with oil. Just block then in the gulf. We could do it. We certainly have the naval power there to do it.

Easton: You have to weigh the cost of doing that. Obviously that would be a huge economic shock.

Barnes: That would be up to the British.

Kondracke: You would think this would offer an opportunity to those in the west --- the president, by the way, has not said a word about it, he's letting Tony Blair handle it --- but this would be an opportunity to rally everybody involved as to the nature of this regime. This is totally blackmail. They are behaving utterly irresponsibly on the nuclear front and on this front and this is the time to put the whammy on them.

Hume: How?

Kondracke: By going to the Europeans and saying now is the time for real sanctions. the Russians don't want to go along but the Europeans, the allies of Tony Blair, could certainly do it.

Hume: You think for the sake of 15 British sailors you could get places like France...?

Kondracke: Right now it's 15 British soldiers, it could be anybody's soldiers, it could be anybody's civilians. This is hostage taking. And it's illegal by every rule of international law. This is an outlaw rogue regime and it ought to be treated like one.

Barnes: It's up to the British to decide. Look, you know President Bush would be glad to be condemning the Iranians every day if Tony Blair said it would help. But remember the British, in the first place, when the Iranians snatched the 15 in Iraqi waters, not Iranian waters, there was a British ship that could have fired on the Iranians. They could have stopped it. And they didn't. And they've followed pretty much a wimpy policy since then. And they haven't gotten anybody back either.