Â鶹ӰÊÓ

A spy plane from Iran has reportedly had an American ship under surveillance -- part of a navy drill which has sparked tensions in a channel that sees one-sixth of the world's oil supply flow through its waters.

Iran's official news agency, IRNA, reported Thursday that the aircraft took photos and video of the U.S. ship during its 10-day exercise in international waters near the Strait of Hormuz.

The straight is strategically positioned in the Persian Gulf as the gateway to the Arabian Sea and the Gulf of Aden.

It was not clear what Iran was hoping to gain from the footage, which was so distant it was hard to make out details of the carrier. Publicity around the footage, however, indicates the country is looking to bolster the image of its navy in the region.

"An Iranian vessel and surveillance plane have tracked, filmed and photographed a U.S. aircraft carrier as it was entering the Gulf of Oman from the Persian Gulf," Adm. Habibollah Sayyari told IRNA told The Associated Press on Thursday.

The naval exercise shows Iran has "control over the moves by foreign forces" in the area, he said, adding the "foreign fleet will be warned by Iranian forces if it enters the area of the drill."

The region also hosts several ships from other countries. The U.S. is about to increase its total there from two to three, and warships from other countries patrol for pirates in the region.

So far, relations between American and Iranian ships in the area remain "professional," U.S. 5th Fleet spokesperson Lt. Rebecca Rebarich told The Associated Press on Thursday.

"Interaction with the regular Iranian Navy continues to be within the standards of maritime practice, well-known, routine," she said.

Rebarich did not address the issued of the surveillance images, news that comes a day after the U.S. government warned Iran was threatening to block off the channel in retaliation over threatened sanctions on its oil exports.

On Wednesday, Iran was defiant as it asserted its right to manage its own interests in the region.

"The U.S. is not in a position" to affect the country's decisions, said the acting commander of Iran's Revolutionary Guard, Gen. Hossein Salami, in local media. "Iran does not ask permission to implement its own defensive strategies."

While Iran's strong words may succeed in drawing attention, American researcher Michael Rubin says the country lacks the capacity to back up its threats.

"It certainly ratchets things up," Rubin, from the conservative American Enterprise Institute think tank, told CTV's Canada AM on Thursday.

"It's bluster, however. On one hand, Iran is capable of closing the Strait of Hormuz. On the other hand, it's only capable of doing it for about a day and it would hurt Iran more than any other country… Not only does Iran have to export oil, it also has to import gasoline."

Suggesting the point of the exercise is more psychological than practical; Rubin said even the threat drives up the price of oil, Iran's main source of revenue. In any case, a blockade of their oil exports would mainly impact Asian consumers, not Americans, he said.

"It's actually the Asian economies that rely on Persian Gulf oil… If Iran really wanted to hurt the western economy, what they'd probably want to do is knock out the southern Iraqi oil fields. Then they could take 2 billion barrels of oil a day off the market."

However, Canadian political scientist Christian Leuprecht said he believes the blockade could cause trouble.

Leuprecht, an associate professor with both Queen's University and the Royal Military College, says isolationist regimes like Iran don't have a great track record for acting rationally, so the argument that a blockade would be too damaging to the country's domestic economy may not hold much water.

"This might not be entirely saber-rattling," he told Â鶹ӰÊÓ Channel on Thursday from Kingston, Ont. "The stakes here are pretty high… If the West pushed them sufficiently, there is enough paranoia and intense isolationism in Tehran that it would be difficult to predict."

It wouldn't be Iran's first skirmish with the west in those waters, he said, noting naval incidents between Iran, American and British troops in 1988, 2003 and 2007 – and said he believed the country could hold the strait for much longer than one day.

"The strategic guesses are that Iran would be able to close the water for two or three days, or up to two weeks," he said, noting 13-15 oil tankers pass through those waters each day.

"The straight is 55 kilometres across but the shipping lane is three kilometres with a three-kilometre buffer on either side… very narrow.

"This would certainly cause havoc on the international oil market."

With files from The Associated Press