LONDON, May 22 (Reuters) - Britain is set to sign a deal ceding sovereignty of the Chagos Islands to Mauritius while also securing the future of the UK-U.S. Diego Garcia military base in the Indian Ocean, media reported on Thursday.

The deal, the details of which were first announced in October, will allow Britain to retain control of the military base on Diego Garcia, the largest island of the archipelago in the Indian Ocean, under a 99-year lease.

British Prime Minister Keir Starmer will join a virtual signing ceremony with representatives from the Mauritian government, the Telegraph newspaper reported.

In 1965 Britain detached the Chagos Islands from Mauritius - a former colony that became independent three years later - to create the British Indian Ocean Territory.

Financial details of the deal have not been set out. Media reports have put the cost to Britain at 9 billion pounds.

U.S. President Donald Trump, who took office in November, indicated his backing for the deal in February after meeting Starmer in Washington. Trump's predecessor Joe Biden had also supported the agreement.

Photo from Reuters