The United States has authorised the deployment of military personnel and resources to Saudi Arabia, the Pentagon says, to provide “an additional deterrent” in the face of “emergent, credible threats” in the region.

The move, agreed in conjunction with the kingdom, aims to boost regional security as tensions in the Gulf mount over Iran’s standoff with the US over sanctions and the 2015 nuclear agreement, and Tehran’s seizure of two British-linked vessels in the strait of Hormuz on Friday.

Saudi Arabia’s defence ministry confirmed the deployment.

“Based on mutual cooperation between Saudi Arabia and the United States of America, and their desire to enhance everything that could preserve the security of the region and its stability ... King Salman gave his approval to host American forces,” a ministry spokesman was quoted by Saudi state news agency SPA as saying.

In June, the Pentagon said it would deploy 1,000 troops to the Middle East but did not say where they were going.

Saudi Arabia has not hosted US forces since 2003 when they withdrew following the end of the war with Iraq. That US presence in Saudi Arabia lasted 12 years, starting with Operation Desert Storm in 1991, when Iraq invaded Kuwait.

As many as 200 US aircraft were stationed at the Prince Sultan air base, around 80 km (50 miles) south of the capital at the peak of the Iraq war, and as many as 2,700 missions a day were handled by the headquarters in Saudi Arabia.

But relations between the two countries were not always easy during the 12 years of cooperation, particularly following the 11 September 2001 attacks in New York which were orchestrated by Saudi-born al-Qaeda leader Osama bin Laden.

Tensions in the Gulf increased further on Friday when Iran said it had seized two British-flagged tankers in the strait of Hormuz.

Iran’s revolutionary Guard claimed to have taken the British-flagged Stena Impero into port after Iranian officials said it had infringed maritime regulations.

The ship’s owners said the vessel had been “approached by unidentified small crafts and a helicopter during transit of the strait of Hormuz while the vessel was in international waters”.

A second tanker, the Mesdar, which is Liberian-flagged but British operated, also made a sudden diversion from its course towards the Saudi port of Ras Tanura on Friday, and tracking data showed it moving northwards towards the Iranian coast before apparently turning off its tracking signal.

Iran’s semi-official news agency, Fars, reported the ship was briefly detained in the strait of Hormuz and given a notice to comply with environmental regulations before being allowed to continue on its way.

The incidents in the strait of Hormuz came as US President Donald Trump insisted that the US military had downed an Iranian drone that was threatening a US naval vessel, despite denials from Tehran.

Agence France-Presse and Reuters contributed to this report