London (AFP) - Britain on Thursday said it would give up sovereignty of a remote Indian Ocean archipelago to Mauritius but will maintain there a strategic military base that it shares with the United States, in what US President Joe Biden described as a “historic agreement”.

The British government has been under pressure for decades to hand over the Chagos Islands to Mauritius, a former colony, but has resisted because of the military base on Diego Garcia island that plays a key role for US operations in the Indian Ocean and Gulf.

“For the first time in more than 50 years, the status of the base will be undisputed and legally secure,” the UK foreign ministry said. A joint British-Mauritian statement said the base would remain open on an “initial” 99-year lease.

Biden hailed the continuation of the base on Diego Garcia – the largest island in the chain – which was notably used during the wars in Afghanistan and Iraq. The base is used by US long range bombers and ships.

“I applaud the historic agreement and conclusion of the negotiations,” Biden said, adding that the site “plays a vital role in national, regional, and global security”.

British Prime Minister Keir Starmer said he spoke to his Mauritian counterpart Pravind Jugnauth, who later said that the deal showed how a small country can “win justice against major powers”.

“Today, 56 years after our independence, our decolonisation is complete. Now our national anthem can sound out even louder across our territory,” he added.

African Union chairman Moussa Faki Mahamat also welcomed the “historic” agreement, saying in a statement on X it “marks a major victory for the cause of Decolonialization, International Law, and the rightful self-determination of the people of Mauritius”.

- Turnaround -

The deal comes after nearly two years of negotiations and marks a significant turnaround after decades of British dismissals of Mauritian sovereignty claims.

At the start of talks in 2023, the two sides agreed that the Diego Garcia military base would continue to operate whatever the outcome.

In 2016, the UK extended the US lease of the military base until 2036.

The joint statement said that Britain and Mauritius would work on a treaty finalising the accord that would ensure Diego Garcia’s operation “well into the next century”.

The treaty could also pave the way for the return of Chagos islanders, who were expelled by the UK in the 1970s as the military base was developed.

But with no permanent population – and with Diego Garcia possibly the only habitable island but remaining off-limits as part of the deal – resettlement looks unlikely.

Britain decided in 1965 to separate the Chagos islands from Mauritius and set up a military base there, which it leased to the United States.

In doing so, it evicted thousands of Chagos islanders who have since mounted a series of legal claims for compensation in the British courts.

The joint statement claims the agreement will “address wrongs of the past” and “support the welfare of the Chagossians”, who were forced to live in exile, including in the UK.

In Mauritius, chair of the Chagos Refugees Group Olivier Bancoult called it a “historic day” but Chagossian Voices, another group representing exiled islanders, said it was excluded from the talks.

“The views of Chagossians, the indigenous inhabitants of the islands, have been consistently and deliberately ignored and we demand full inclusion in the drafting of the treaty,” Chagossian Voices added.

In Britain, politician James Cleverly, who is bidding to become the new leader of the opposition Conservatives party, called the deal “weak, weak, weak”, even though he initiated the sovereignty talks when he was foreign secretary.

His Tory party leadership rival Robert Jenrick called it a “surrender”.

- Mounting pressure -

Mauritius has claimed the archipelago – renamed the British Indian Ocean Territory – since its independence in 1968 and has garnered increased international support.

In 2019 the International Court of Justice advised Britain to hand over the remote islands. During the hearings, the UK apologised for the “shameful” eviction of islanders, but ignored the ICJ ruling at the time.

The same year, the UN General Assembly also passed a resolution calling on Britain to “withdraw its colonial administration”.

Without the agreement, “the long-term, secure operation” of the military base would be under threat, including through legal challenges posed by international courts, Britain’s foreign ministry said.

“Today’s agreement secures this vital military base for the future,” Foreign Secretary David Lammy said, adding that the deal would also shut down the potential for the islands to be used as a “dangerous illegal migration route to the UK”.

In addition, the UK announced a “package of financial support” to Mauritius including an annual payment and an infrastructure partnership.

The statement claimed that the agreement resolves “all outstanding issues between the United Kingdom and Mauritius”.

It said the two countries would also cooperate on environmental and irregular migration.

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