The United Kingdom Foreign Office on Thursday said it had reached an agreement to hand over the rule of the Chagos Islands to Mauritius.

It said the status agreement secured the long-term status of a strategic military facility used by both British and US forces on the largest island of Diego Garcia.

The UK began negotiations over the Chagos Islands, also known as the British Indian Ocean Territory, in 2022.

Why did the UK agree to this?

The United Nations' highest court, the International Court of Justice, previously declared the UK's administration of the islands "unlawful" and said it must end.

To make way for the military base, native Chagossians were forced to leave the central Indian Ocean territory by 1973.

Those expulsions are seen as one of the most unjust episodes in Britain's modern colonial history. Chagossians have fought for decades to be able to return to the islands.

UK Foreign Minister David Lammy said the agreement meant the status of the base would be legally secure.

"This government inherited a situation where the long-term, secure operation of the Diego Garcia military base was under threat, with contested sovereignty and ongoing legal challenges."

"Today's agreement secures this vital military base for the future."

"It will strengthen our role in safeguarding global security, shut down any possibility of the Indian Ocean being used as a dangerous illegal migration route to the UK, as well as guaranteeing our long-term relationship with Mauritius, a close Commonwealth partner."

US President Joe Biden welcomed the agreement as "historic" and said it ensured the "effective operation of the joint facility on Diego Garcia into the next century."

The office of British Prime Minister Keir Starmer said he spoke to his Mauritius counterpart, Pravind Jugnauth, on Thursday morning, welcoming the agreement. It followed two years of negotiations that started under the previous Conservative administration.

What did Mauritius say?

"Fifty-six years after our independence, the decolonization is finally complete," Jugnauth said in a televised address on Thursday.

The Mauritius government said that the treaty would seek to resolve all outstanding issues related to the islands, as well as addressing "the wrongs of the past."

Resettlement of the Chagos appears unlikely. Under the terms of the deal, the only habitable island remains off-limits.

Mauritius Foreign Minister Maneesh Gobin said it had been "a day to remember" and the development was a "seminal moment" in Mauritius's relationship with former colonial power Britain.

Conservative lawmakers vying to lead Britain's opposition party expressed dismay at the decision to hand over sovereignty of the islands.

Critics have also said the move could benefit China, which maintains close trade ties with Mauritius.

Why is the base so strategic?

The base on Diego Garcia, the largest island, gained major strategic importance during the Cold War as an assertive Soviet navy affirmed its presence in the Indian Ocean.

It also offered proximity to the Middle East and Asia.

After the 1979 revolution in Iran, the US expanded the military hub, allowing it to receive more warships and heavy bombers.

More recently, the facility served as a staging ground for US bombing campaigns in Afghanistan and Iraq.

rc/msh (AFP, AP, dpa, Reuters)