U.S. Defense Secretary Robert M. Gates is expected this week to approve a request by commanders for a second aircraft carrier and its supporting ships to be stationed within quick sailing distance of Iran by early next year, according to the report.

Senior U.S. military officers were quoted as saying that the increase in naval power should not be viewed as preparations for any offensive strike against Iran.

However, they acknowledged that the ability to hit Iran would be increased and that Iranian leaders might well call the growing presence provocative.

One purpose of the deployment, they said, is to make clear that "the focus on ground troops in Iraq has not made it impossible for the United States and its allies to maintain a military watch on Iran."

That would also reassure Washington's allies in the region which are concerned about Iran's intentions, said the officers.

Meanwhile, the British navy also plans to add two mine-hunting vessels to the Gulf.