The United States is keeping the pressure on Iran with the presence of two aircraft carriers close to the Gulf region ahead of the resumption of nuclear talks with Tehran this week.

"There are currently two carrier strike groups in the US 5th Fleet area of operations," Lieutenant Commander John Fage, a navy spokesman, said Monday.

"USS Abraham Lincoln is currently in the north Arabian Sea (not in the Gulf region itself) and USS Enterprise is transiting the Gulf of Aden."

The Enterprise has in effect replaced the USS Carl Vinson, which has left the zone to conduct maneuvers in the Bay of Bengal before later returning to the west coast of the United States.

The US naval presence in the Gulf is described as routine by the Pentagon, but tensions have risen in recent months following Iran's threat to close the Strait of Hormuz, a key global oil chokepoint in the region.

In January, Pentagon chief Leon Panetta said the United States was "fully prepared" for any confrontation with Iran over the Strait of Hormuz, but said he hoped a dispute would be resolved peacefully,

Tehran threatened last December to close the strait -- where one-fifth of the world's traded oil passes through -- in the event of a military strike or severe tightening of international sanctions over its disputed nuclear program.

Iran on Monday confirmed that nuclear talks this week with world powers would take place in Istanbul, dropping public reservations over that city as the venue following a sharply worded row with Turkey.

Iran last held talks with the so-called P5+1 powers -- permanent UN Security Council members Britain, China, France, Russia and the United States plus Germany -- in January 2011 with no results.