The U.K. government is seeking to determine whether U.S. President Donald Trump has the power to derail its plans to hand over sovereignty of a strategically vital island to Mauritius, after Trump called into question a deal he had previously backed.

Ministers are also trying to establish if the U.S. administration intends to veto the deal over the Chagos Islands, according to a person familiar with the matter, who requested anonymity speaking about a diplomatically sensitive topic. They said that if the U.S. does change its long-held position, it would likely be enough to unravel the agreement.

Under the deal brokered by U.S. Prime Minister Keir Starmer¡¯s government, the U.K. will lease back a joint U.S.-U.K. military base on Diego Garcia from Mauritius for 99 years. After supporting the agreement last year, Trump last week called it an ¡°act of total weakness¡± and ¡°great stupidity.¡± That¡¯s despite his own previous support and U.S. Secretary of State Marco Rubio¡¯s description of the deal as a ¡°monumental achievement.¡±