ABU DHABI/RIYADH - Forces from the United Arab Emirates have rescued a British hostage held for more than 18 months by Al-Qaeda in Yemen, authorities in Abu Dhabi and London said on Sunday.

Douglas Robert Semple, a 64-year-old oil worker, had been kidnapped by Al-Qaeda in February 2014 while working in Yemen's Hadramawt province, a stronghold of the jihadist group, a statement carried by the UAE's official WAM news agency said. It said that UAE forces freed Semple in a military operation on Saturday and took him to Yemen's main southern city of Aden, from where he was flown to Abu Dhabi overnight.

Emirati forces are among troops taking part in a Saudi-led campaign supporting Yemen's government against Iran-backed rebels. The statement provided no details about the operation or where Semple had been held. Four suspected Al-Qaeda militants were killed overnight in an apparent US drone strike in Mukalla, the southern Yemeni city that the extremist group overran in April, a local official said Sunday.

The four were travelling in a car on the tarmac of Mukalla's Al-Rayane airport that was struck by a missile fired by an "American drone", according to the unnamed official, killing them instantly.

The night strike follows a similar attack on Friday which killed three Al-Qaeda suspects as they travelled through the central Marib province, tribal sources said. A Saudi border guard has been killed by rocket fire from anti-government rebels in northern Yemen, Riyadh's official SPA news agency said on Sunday. A border post in the kingdom's Jazan region came under attack on Saturday, prompting guards to respond to the fire, the SPA said, quoting an interior ministry spokesman. It said one Saudi guard was killed in the exchange. The Foreign Office in London confirmed that a British hostage in Yemen had been freed by UAE forces but did not identify him and also provided no further details.

"I'm pleased to confirm that a British hostage held in Yemen has been extracted by UAE forces in a military intelligence operation," Foreign Secretary Philip Hammond said in a statement released while he was in Tehran to reopen the British embassy.

Hammond said the freed hostage was "safe and well" and that Britain was "very grateful for the assistance of the UAE". The statement carried by WAM said Semple had been met at the airport in Abu Dhabi by UAE officials and the British ambassador.

He was taken to hospital for health checks and spoke to his wife by telephone, it said. He was to leave for Britain following the medical checks.

WAM said Abu Dhabi's Crown Prince Sheikh Mohammed bin Zayed al-Nahyan had telephoned British Prime Minister David Cameron on Saturday night to inform him of the operation.

Cameron later Tweeted: "I'm so pleased for the family of the British hostage in Yemen - who has been released safe and well. Thanks to the UAE for their help." The UAE, a longtime Western ally, is a key partner in the Saudi-led coalition that in March launched air strikes against the Huthi rebels as they advanced on Aden, forcing President Abedrabbo Mansour Hadi's government to flee to Riyadh.

The Huthis had seized the capital Sanaa last September. The coalition has also provided military equipment to loyalist forces and reportedly sent troops, with Saudi media reporting that some 1,500 soldiers, most from the UAE, had entered Aden.

The statement carried on WAM was the first official confirmation that UAE troops were on the ground in Yemen. "This action by the UAE forces in Aden is renewed evidence of the UAE's unchanging policy towards terrorism in all of its forms," the statement said.

Backed by the coalition, pro-government forces retook Aden in mid-July and in recent weeks have been pressing a major offensive against the rebels.

As well as Aden, they have recaptured four other southern provinces and in recent days have fought fierce battles for control of Yemen's third-largest city, Taez.

The conflict has killed more 4,500 people since March, according to the United Nations.

Kidnapping has long been rife in Yemen, with hostages often used as bargaining chips between rival groups.

Earlier this month French hostage Isabelle Prime arrived in Oman following her release in Yemen after nearly six months of captivity.

Last year British teacher Mike Harvey was released after being held for five months in Yemen following negotiations.

In December, US journalist Luke Somers and South African teacher Pierre Korkie died during a failed attempt by US commandos to rescue them from an Al-Qaeda hideout in southeastern Yemen.

Al-Qaeda in the Arabian Peninsula (AQAP), the local branch of the jihadist network, is considered among its most dangerous affiliates and has taken advantage of the chaos in Yemen to seize territory including Hadramawt provincial capital Mukalla.

AQAP was behind several plots against Western targets, including this year's deadly attack on French magazine Charlie Hebdo.