Updated 4:21 PM ET
TEHRAN, Iran - Iran continued to suggest it may block the Strait of Hormuz in response to greater international pressure over its nuclear program, rejecting a U.S. warning that any attempt to choke off the key oil supply route would not be tolerated.
"The U.S. is not in a position" to affect Iran's decisions, Gen. Hossein Salami, the acting commander of Iran's Revolutionary Guard told the semi-official Fars news agency Thursday. "Iran does not ask permission to implement its own defensive strategies."
Iran had previously threatened the close the strait if Washington imposes sanctions targeting Iran's crude exports. On Wednesday, Lt. Rebecca Rebarich, a spokeswoman for the Bahrain-based U.S. 5th Fleet, said the Navy was "always ready to counter malevolent actions to ensure freedom of navigation."
Meanwhile, official IRNA news agency reported an Iranian surveillance plane has recorded video and photographed a U.S. aircraft carrier during Iran's ongoing navy drill near a strategic waterway in the Persian Gulf.
The report did not provide details and it was unclear what information the Iranian military could gleam from such footage. But the announcement is an indication Iran is seeking to cast its navy as having a powerful role in the region's waters.
IRNA quoted Iran's navy chief, Adm. Habibollah Sayyari, as saying the action shows that Iran has "control over the moves by foreign forces" in the area where Tehran is holding a 10-day military exercise.
"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," Sayyari said.
He added that the "foreign fleet will be warned by Iranian forces if it enters the area of the drill."
State TV showed what appeared to be the reported video, but it was not possible to make out the details of the carrier because the footage was filmed from far away.
The Iranian exercise is taking place in international waters near the Strait of Hormuz the passageway for one-sixth of the world's oil supply.
Beyond it lie vast bodies of water, including the Arabian Sea and the Gulf of Aden. The U.S. Navy's 5th Fleet is also active in the area, as are warships of several other countries that patrol for pirates there.
Lt. Rebarich said the aircraft carrier USS John C. Stennis and guided-missile cruiser USS Mobile Bay headed out from the Gulf and through the Strait of Hormuz on Tuesday, after a visit to Dubai's Jebel Ali port.
She described the passage through the strait as "a pre-planned, routine transit" for the carrier, which is providing air support from the north Arabian Sea to troops in Afghanistan.
Rebarich did not directly address Iranian claims of possessing the reported footage but said the 5th Fleet's "interaction with the regular Iranian Navy continues to be within the standards of maritime practice, well known, routine and professional."
That Iran is making such dire threats at all illustrates its alarm over new sanctions planned by the U.S. that will target oil exports the most vital source of revenue for its economy. Iran's leaders shrugged off years of past sanctions by the U.S. and United Nations, mocking them as ineffective. But if it cannot sell its oil, its already-suffering economy will be sent into a tailspin.
"It would be very, very difficult for Iran even to impede traffic for a significant period of time," said Jonathan Rue, a senior research analyst at the Washington-based Institute for the Study of War. "They don't have the ability to effectively block the strait."
What the Iranians can do, Rue and other analysts say, is harass traffic through the Gulf anything from stopping tankers to outright attacks. The goal would be to panic markets, drive up shipping insurance rates and spark a rise in world oil prices enough to pressure the United States to back down on sanctions.
The strait would seem to be an easy target, a bottleneck only about 30 miles (50 kilometers) across at its narrowest point between Iran and Oman.
Tankers carrying one-sixth of the world's oil supply pass through it, from the fields of petrogiants Iran and its Gulf Arab neighbors, exiting the Persian Gulf into the Arabian Sea and on to market. They move through two two-mile-wide shipping lanes, one entering the Gulf, one exiting.
In recent years, Iran has dramatically ramped up its navy, increasing its arsenal of fast-attack ships, anti-ship missiles and mine-laying vessels. Its elite Revolutionary Guards boasts the most powerful naval forces, with approximately 20,000 men, with at least 10 missile patrol boats boasting C-802 missiles with a range of 70 miles (120 kilometers) and a large number of smaller patrol boats with rocket launchers and heavy machine guns, according to a recent report by Anthony Cordesman at the Center for Strategic and International Studies.
The navy has three submarines and an unknown number of midget subs, capable of firing "smart" torpedoes or laying mines. It also has a large scale capability for laying mines using both small craft and commercial boats, according to the report.
The Revolutionary Guard has also deployed a heavy array of anti-ship Seersucker missiles with a range of up to 60 miles (100 kilometers) along its coast overlooking the strait, on mobile platforms that make them harder to hit.
The Guard's naval forces and the regular navy "have been the most favored service. The Iranian air force and ground forces have not seen the same level of attention in domestic procurement and weapons systems," Rue said. "They realize their navies are the best options for inflicting casualties" on the U.S. or Arab Gulf nations.
Still, those forces would not likely be enough to outright seal the strait, given the presence of the U.S. 5th Fleet based in the Gulf nation of Bahrain. On Wednesday, Pentagon spokesman George Little warned that any "Interference with the transit or passage of vessels through the Strait of Hormuz will not be tolerated."