MANAMA (AFP) - Britain on Thursday (April 5) opened a new naval base in Bahrain, its first permanent military outpost in the Middle East in nearly half a century, London's defence ministry said.

The base, south of Bahrain's capital Manama, will house around 300 British troops and support personnel as Britain and Gulf states press their campaign against militant groups in the region.

"Our presence in Bahrain will play a vital role in keeping Britain safe as well as underpinning security in the Gulf," defence secretary Gavin Williamson said.

Bahrain and Britain are part of the US-led coalition battling the Islamic State group in Syria and Iraq, and the new base means Britain will have the opportunity to add to its four mine-hunter warships currently based at the Mina Salman port.

"What happens in the Gulf region has a direct impact on the national security of the United Kingdom, our prosperity and the safety of our citizens," Britain's defence ministry said.

"It is vital that we work with close allies like Bahrain to tackle regional threats such as that posed by Daesh," it added, using an Arabic acronym for ISIS.

The tiny island nation of Bahrain currently houses the US Navy's Fifth Fleet.

Britain withdrew from bases in the Gulf in 1971 as part of its plan to pull out from "East of Suez".

It ended its troop presence in southern Iraq in 2009, leaving bases built in Basra after the 2003 invasion.