WASHINGTON, April 2: The tensions between the United States and Iran took yet another twist on Monday when Washington asked Tehran to provide information about an American who went missing in Iran several weeks ago.

Earlier on Monday, a government spokesman in Tehran claimed that the US war planes had violated Iranian airspace in the oil-rich province of Khuzestan.

On Saturday, US President George Bush called Iran's seizure of 15 British sailors and marines last week an “inexcusable behaviour” and demanded that the “hostages” be released, weighing in for the first time as the situation escalates into a sustained confrontation with Tehran.

He rejected any “quid pro quo” trade of Iranians held by US forces in Iraq and ducked a question about whether military force would be justified to free the captured sailors.

At a regular briefing on Monday, State Department spokesman Sean McCormack told reporters that the US was sending an official inquiry to Iran about an American whose family and employer reported him missing.

The US has already sent the inquiry request to Swiss diplomats who act as a go between with Tehran because the two countries do not have diplomatic relations.

Mr McCormack emphasised the American was in Iran on private business and was not working for the US government. He is believed to have gone missing on Kish Island off the southern coast of Iran.

“We don’t see any linkage between this case and any ongoing cases in the news recently,” Mr McCormack said, referring to the British sailors now in Iran’s custody.

Mr McCormack declined for privacy reasons to provide further information on the American except to say the United States had been monitoring the situation for several weeks but had not so far found any information on his whereabouts.

In Tehran, the state-run TV station Al-Alam quoted a military spokesman, Col Aqili, as saying that “two airplanes flew through Iranian airspace in the northwest of Abadan, before heading southwest towards Iraq.”

On Sunday, the same television channel broadcast the footage of the British naval personnel pointing to a map of the Persian Gulf. The report said that the two sailors were indicating the point where their ship entered Iranian waters on March 23, which led to their arrest.

Also during the weekend, hundreds of students gathered in front of the British embassy, throwing stones at the building and demanding the expulsion of the ambassador.

Diplomats in Washington see no early resolution to the dispute over the British sailors, noting that both the British and Iranian governments were fighting their cases in public - a move that significantly reduces the chance of a quick settlement. They point out that the US does not have much leverage on Iran to persuade it to release the sailors or find and return the missing American.

Earlier this year, when the Iraq Study Group and Congress pushed the White House to recognize the need for diplomacy with Iraq's neighbors, including Iran, the administration acknowledged that it does not have much room for diplomacy.

“Frankly, right at this moment there's really nothing the Iranians want from us, and so in any negotiation right now we would be the supplicant,” Secretary of Defence Robert Gates explained. “The only reason to talk to us would be to extract a price, and that's not diplomacy, that's extortion.”