A US navy ship due for decommissioning has been sent to the Arabian Gulf to help mine-clearing operations.
The deployment is the latest move in a gradual US build-up as tensions with Iran smoulder.
A spokesman for the US Fifth Fleet, based in Bahrain, said the USS Ponce, described as an "afloat forward staging base [AFSB]", had arrived on Thursday after undergoing refitting.
The move comes as the chairman of the Iranian military's Joint Chiefs of Staff said Tehran would block the Strait of Hormuz, through which 40 per cent of the world's seaborne oil exports flow, if it determined that the Islamic republic's interests were seriously threatened.
Gen Hasan Firouzabadi's comments yesterday to Iranian media came less than a week after the European Union imposed an embargo on Iran's vital oil sector to pressure Tehran over its disputed nuclear programme.
The US and its allies accuse Iran of seeking nuclear weapons - a charge Tehran denies.
Gen Firouzabadi did not specify what would constitute a threat to Iran's interests, and did not mention the new EU sanctions.
But Iran's Revolutionary Guard has warned in the past that it would close the strait if Tehran's oil exports are blocked.
Four US minesweepers arrived in the Arabian Gulf last month to bolster the Fifth Fleet and ensure the safety of shipping routes.
* Reuters and the Associated Press
