Tehran's threat to block crude shipments through the crucial passage for Middle Eastern suppliers followed the European Union's decision to tighten sanctions on Iran over its nuclear program, as well as accompanying moves by the United States to tighten unilateral sanctions.

Iran's English-language Press TV quoted Hossein Salami as saying: "Any threat will be responded by threat ... We will not relinquish our strategic moves if Iran's vital interests are undermined by any means."

Separately, Salami was quoted as saying by the official IRNA news agency: "Americans are not in a position whether to allow Iran to close off the Strait of Hormuz."

The US Fifth Fleet said Wednesday it would not allow any disruption of traffic in the Strait of Hormuz, a strip of water separating Oman and Iran.

The official IRNA news agency reported Thursday that an Iranian surveillance plane has recorded video and photographed a US aircraft carrier during Iran's ongoing navy drill near the strait.

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 US 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."

The Iranian exercise is taking place in international waters near the Strait of Hormuz. The US Navy's Bahrain-based 5th Fleet is also active in the area, as are warships of several other countries that patrol for pirates there.