Iran's navy has sent submarines to the Red Sea "to collect data," its first mission in distant waters, the Fars news agency reported Tuesday without giving further details.

"The submarines, dispatched in May, have entered the Red Sea after a mission in the Gulf of Aden to collect data on the sea bed in the high seas and to identify other warships," Fars said quoting an unnamed source.

"They are accompanying an Iranian navy fleet," it added, without mentioning the number of the submarines, their types or the make of the fleet.

The Pentagon confirmed the movement of the Iranian submarines on Tuesday and said the United States is not "concerned" at this time.

"We've repeatedly expressed our concerns with the actions that lead to instability but just moving forces around isn't necessarily something that we're concerned with," said Pentagon spokesman Colonol David Lapan.

He added that how Iran uses its forces in the region is of interest for the Pentagon. "It always has to do with what their intentions are," he said.

Iran has several types of submarines, including the home-produced 500-tonne Nahang which was first introduced to the navy in 2006, as well as three Russian-made submarines of the Kilo class purchased in the 90s.

In August 2010, Iran's army chief Ataollah Salehi announced the inauguration of a new "semi-heavy" submarine, named Qaem, capable of operating in the high seas, such as the Indian Ocean or the Gulf of Aden.

Iran's navy operates 11 mini submarines of the domestically built 120-tonne Ghadir class, first launched in 2007, which according to Iranian officials are "stealth" submarines and patrol shallow waters, notably the Gulf.

Last February, two Iranian warships were sent to the Mediterranean Sea for a visit to Syria, crossing the Red Sea and Suez Canal, a move that angered Israel.

The two ships docked in Syria on February 24, marking Iran's first such mission since the 1979 Islamic revolution.

Tel Aviv put its navy on alert, following the entry of the Iranian vessels in the Mediterranean, while Israeli President Shimon Peres described the move as a "political provocation."