Questions Raised About UK Agreement on Mauritius Base

January/February 2025
By Shizuka Kuramitsu

The United Kingdom has agreed to cede the disputed Chagos Islands to Mauritius in a deal that the UK and the United States say will ensure that the strategically important military base at Diego Garcia remains in their control for at least the next 99 years.

Under terms reached on Oct. 3, the UK agreed that Mauritius should have sovereignty over the Chagos Islands in the central Indian Ocean. This will include Diego Garcia, the largest island in the archipelago, which serves as a joint UK-U.S. military base. Diego Garcia carries strategic importance because of growing U.S. competition with China in the Pacific region and Chinese ties with Mauritius.

In a joint statement, Mauritius and the UK said that their “political agreement is subject to the finalisation of a treaty and supporting legal instruments, which both sides have committed to complete as quickly as possible.” But it still may face political hurdles given questions raised by skeptical politicians in Washington, London, and Port Louis.

“Under the terms of this treaty the United Kingdom will agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia,” the joint statement said.

“At the same time, both our countries are committed to the need, and will agree in the treaty, to ensure the long-term, secure and effective operation of the existing base on Diego Garcia, which plays a vital role in regional and global security,” the statement said.

The agreement authorizes the UK to exercise sovereign rights over Diego Garcia for an initial period of 99 years and requires Mauritius “to ensure the continued operation of the base well into the next century.”

Several countries and organizations, including the United States, India, the African Union, and the United Nations welcomed the outcome of the Mauritian-UK negotiations, which took two years.

U.S. Secretary of State Antony Blinken, applauding the agreement, emphasized the strategic value of keeping Diego Garcia under UK-U.S. jurisdiction. “This agreement will secure the operational future of the joint U.S.-UK military facility on Diego Garcia into the next century. Diego Garcia plays a vital role in U.S. efforts to establish regional and global security, respond to crises, [and to] counter some of the most challenging security threats of our time,” Blinken said in press statement on Oct. 3.

In a statement on Oct. 3, Moussa Faki Mahamat, chairperson of the African Union Commission, also hailed the agreement as a “significant milestone [that] marks a major victory for the cause of Decolonization, International Law, and the rightful self-determination of the people of Mauritius, bringing an end to decades of disputes.”

It commended “both Parties for honoring their international obligations based on the rules of law and justice” and called on them “to expedite the finalization of the legal aspects of the Agreement in order to allow Mauritius to exercise its full sovereignty over the islands.”

Despite this, diplomatic tension over the agreement is high. According to news reports, U.S. President-elect Donald Trump, his advisers, and Republican members of Congress have questioned the possible impact of the agreement on U.S. security interests and expressed concerns that the agreement benefits China.

Sen. Marco Rubio (R-Fla.), whom Trump nominated to be secretary of state, told Politico in October that the handover of the Chagos Islands “would provide an opportunity for communist China to gain valuable intelligence on our naval support facility in Mauritius.”

“This poses a serious threat to our national security interests in the Indian Ocean and threatens critical U.S. military posture in the region,” he said.

In recent years, China has increased its presence in the region, including establishing a military base in Djibouti in 2017 and signing a free trade agreement with Mauritius in 2021. Since 2019, there also has been talk of Russia attempting to establish a naval base in Sudan.

Further, Mauritius is a state-party to the Treaty of Pelindaba, which established the African nuclear-weapon-free zone and commits states-parties “to prohibit, in its territory, the stationing of any nuclear explosive device.” The treaty also asserts that “each Party in the exercise of its sovereign rights, remains free to decide for itself whether to allow visits by foreign ships and aircraft to its ports and airfields, transit of its airspace by foreign aircraft, and navigation by foreign ships in its territorial sea or archipelagic waters in a manner not covered by the rights of innocent passage, archipelagic sea lane passage or transit passage of straits.”

The UK and the United States are nuclear-weapon states, and the ships, submarines, and aircraft that they either base or periodically land at Diego Garcia may carry nuclear weapons.

During a Dec. 2 debate in the UK Parliament, opposition Conservative Party members asked about negative security impacts of the treaty, but Luke Pollard of the Labour Party dismissed their concerns. “[T]he long-term protection of the base on Diego Garcia has been the shared UK and U.S. priority throughout, and this agreement secures its future,” he said. “We would not have signed off on an agreement that compromised any of our security interests, or those of the U.S. and our allies and partners.”

Nevertheless, the Conservative Party’s shadow defense secretary, James Cartlidge, has asked for further clarification on how the deal affects UK and U.S. operations in Diego Garcia, including those involving nuclear weapons, according to The Independent on Dec. 8.

“We need urgent clarity from the government on whether we, and the U.S., will have full military autonomy on Diego Garcia, after Labour’s new settlement kicks in,” he said. “[W]ill our ability to operate be wholly sovereign or subject 
to new rules that threaten our freedom of operation?”

“We already have a confused position and lack of transparency on the cost of the new deal. Far too many questions remain unanswered for such an important issue,” Cartlidge said.

The deal also is coming under pressure from newly elected Mauritian Prime Minister Navin Ramgoolam, who took office in November. He told members of the Mauritian Parliament that he is renegotiating the deal by submitting counterproposals.

According to reports by Reuters and other media, Ramgoolam said that the current deal “would not produce the benefits that the nation could expect from such an agreement” and that his government “is still willing to conclude an agreement.”

A spokesperson for UK Prime Minister Keir Starmer, playing down the idea of a rift, told The Guardian on Dec. 17 that “it makes sense that we would engage with the new administration on the details of the deal.”

Mauritius has long argued that the UK forced it to give the Chagos Islands away in return for its own independence from the UK in 1968. Two years earlier, London concluded a secret deal with Washington to lease Diego Garcia for use as a military base in return for a $14 million discount off the purchase of U.S. Polaris ballistic missiles for UK submarines, according to an article from 1975 in The New York Times. As part of this deal, the UK forcibly expelled 1,500 to 2,000 islanders from the archipelago.

With its well-equipped capability to host U.S. nuclear-armed heavy bombers and submarines, Diego Garcia has served as a strategic military asset for the UK and the United States, including as a staging point for operations in Afghanistan and Iraq after 9/11.