Donald Trump has issued a forceful warning to Prime Minister Keir Starmer over the United Kingdom’s agreement to transfer sovereignty of the Chagos Islands to Mauritius while retaining use of the strategic Diego Garcia military base.

In a post on his social media platform, Trump described the long-term lease arrangement as “a big mistake” and urged London not to “give away” control of the Indian Ocean territory, suggesting the base could be essential in any future military operations should tensions with Iran escalate.

The Chagos sovereignty deal, finalised in 2025, envisages the UK ceding formal sovereignty over the archipelago to Mauritius while negotiating a 99-year lease to continue operating the joint UK-US base on Diego Garcia.

The arrangement was broadly supported by the US State Department and seen as a way to secure the base’s future amid legal challenges over the territory’s status, and has also received backing from the United Nations and other international actors as part of decolonisation efforts.

Trump’s latest comments mark yet another reversal in his public stance on the matter.

Earlier this year he called the transfer an “act of great stupidity,” then appeared to accept the deal as the best outcome following discussions with Starmer, and most recently reaffirmed his opposition, warning that relinquishing control of Diego Garcia could undermine allied security interests.

Trump framed his critique against the backdrop of heightened tensions with Iran and broader geopolitical competition, asserting that retaining direct allied control over key bases is vital for deterrence and rapid response.

The UK government has defended the agreement, emphasising that the deal’s leaseback provisions guarantee continuity of military operations and are crucial to national and allied security.

London has stressed that the arrangement resolves longstanding legal and diplomatic disputes over the archipelago’s status while safeguarding its strategic footprint in the Indo-Pacific and Indian Ocean regions.

British officials have also reiterated commitments to the welfare and potential return of displaced Chagossian communities, whose removal to make way for the base in the 1960s remains a persistent source of legal challenge and moral debate.

Observers note that Trump’s public oscillation on the issue — coupled with official US policy statements backing the UK-Mauritius deal — highlights a degree of unpredictability in Washington’s approach to allied defence cooperation.

The dispute underscores broader strains in transatlantic relations as London navigates strategic commitments amid shifting geopolitical pressures, including China’s rising influence and ongoing negotiations over Iran’s regional posture.

The debate over Diego Garcia and the Chagos Islands is likely to remain a focal point as both governments seek to balance historical obligations, military imperatives and alliance unity.