Washington: An ageing American naval ship converted into a “floating base” has arrived off the coast of Bahrain to support counter-mine operations in the Gulf, the US Navy said Friday.

The deployment of the USS Ponce marks the latest in a gradual build-up of American forces in the region since tensions spiked with Iran in December over its nuclear programme, with Tehran threatening to possibly close the strategic Strait of Hormuz.

Equipped with a helicopter landing deck and space for troops, the amphibious transport ship, in service since 1971, can support an array of missions as a “forward staging base” involving special forces, countermine operations or repair work for warships, officials said.

The Ponce “provides us with an enhanced capability to conduct maritime security operations, and gives us greater flexibility to support a wide range of contingencies with our regional parters,” said Vice Admiral John Miller, commander of naval forces in the Middle East.

The ship, which has a crew of 150 civilians and 55 sailors, departed Norfolk, Virginia on June 1 and arrived in Bahrain on Thursday, officials said.

Apart from the Ponce, the Navy has deployed two aircraft carriers to the region - the USS Abraham Lincoln and the USS Enterprise - and doubled its mine sweeper fleet in the area from four to eight ships on June 23.

Four MH-53 Sea Stallion helicopters also were deployed in March to back up counter-mine efforts and the US Air Force in April moved radar-evading F-22 fighter jets to the United Arab Emirates.

The increased US military presence - including the mine sweepers - is meant to send a clear message to Iran over its threats to mine the narrow Strait of Hormuz, through which about a fifth of the world’s traded oil passes.