Aircraft crowd the flight deck of the aircraft carrier USS Nimitz as the guided-missile cruiser USS Princeton accompanies the Nimitz through the Strait of Hormuz. Iran is threatening to close the strait, through which some 16 million barrels of crude pass each day. Image Credit: Bloomberg

Washington: The Pentagon said on Friday that Iran's "destabilising behaviour" was a factor in its planning in the Middle East, but sought to discourage speculation the US military was quietly building up forces in the region to counter any perceived threat.

The number of US forces in Kuwait has grown to about 15,000 in recent weeks, including two combat brigades, as troops have withdrawn from Iraq following the end of the war there.

Navy Captain John Kirby, a Pentagon spokesman, said he was not aware of any decision to permanently increase the number of troops based in Kuwait.

The US force there has expanded temporarily because a brigade deployed to Iraq at the end of the war had been shifted to Kuwait to finish its deployment, he said.

Force numbers in any given location shift regularly depending on needs, Kirby said.

"I'm not aware of any plus-up that's been ordered into Kuwait. And I don't think the numbers would bear out that there is, in fact, a huge plus-up in Kuwait," he told reporters.

Second aircraft carrier

Earlier this week, the military said a second aircraft carrier had arrived in the Arabian Sea and a third was on its way to the region. The Pentagon portrayed this as a normal rotation, with one ship en route to its home port. Kirby said it was not unusual to have two carriers in the region.

The movements come at a time of heightened tensions between the United States and Iran. Iran has threatened action if another US carrier moves into the Gulf and has said it might try to close the Strait of Hormuz. Defence Secretary Leon Panetta has warned that any such action would be a red line, requiring a US response. But, Kirby sought to downplay reports that "we're ramping up presence in the Middle East because of Iran".

‘Destabilising behaviour'

"Iran is certainly a factor in our discussions with our allies and in our thinking about the future of the Middle East — there's no question about it — thanks to their destabilising behaviour," Kirby told reporters at the Pentagon.

"But I want to disabuse everybody of the notion that there's some kind of quiet increase going on, specifically aimed at some sort of contingency planning for any one country in that part of the world," he commented.

Panetta has said the United States would have about 40,000 troops in the region after the withdrawal of American forces from Iraq at the end of 2011. Kirby declined to specify where they would all be located.