Pope Leo XIV has said he is “delighted” the UK has agreed to hand the Chagos Islands to Mauritius.

Speaking to a delegation of 15 refugees from Chagos, Pope Leo said that the move represented a “significant victory” in their long battle to “repair a grave injustice”.

Under the terms of a treaty signed in May, Mauritius will gain sovereignty of the islands from the UK, but allow the US and UK to continue operating a military base on one of the islands, Diego Garcia, for an initial period of 99 years.

The Pope said he hoped Mauritian authorities would ensure the refugees are able to return home. UK opposition leaders – and some Chagossians now resident in the UK – have criticised the deal.

Speaking in French, the pontiff said: “The renewed prospect of your return to your native archipelago is an encouraging sign and a powerful symbol on the international stage.”

He added that all people “must be respected by the powerful in their identity and rights, in particular the right to live on their land – and no one can force them into exile”.

A UK government spokesperson said the military base on Diego Garcia was “essential” to the security of the UK and its allies.

“This deal secures the operations of the joint US-UK base for generations, with robust provisions for keeping its unique capabilities intact and our adversaries out,” they added.

The UK purchased the islands for £3m in 1968, but Mauritius has argued it was illegally forced to give away the islands in order to gain independence from the UK.

The islands were then cleared to make way for a UK-US armed forces base with large groups of Chagossians moving to Mauritius and the Seychelles, or taking up an invitation to settle in England, mainly in Crawley, West Sussex.

In May, the government said it would pay Mauritius an average of £101m a year for 99 years under the terms of the agreement.

The deal sets a 24-mile buffer around Diego Garcia, where nothing can be built without UK consent.

Foreign military and civilian forces will also be barred from other islands in the archipelago, with the UK retaining a power to veto any access to the islands.

The treaty will come into effect only after it is approved by both the UK and Mauritian parliaments.

When the deal was struck, the Conservatives described it as “an act of national self-harm”, which left the UK “more exposed to China” because of its ties with Mauritius.

The prime minister insisted that the deal was imperative to maintaining the UK’s national security.

“If we did not agree this deal the legal situation would mean that we would not be able to prevent China or any other nation setting up their own bases on the outer islands or carrying out joint exercises near our base,” Sir Keir Starmer said.

“No responsible government could let that happen.”

The agreement was welcomed by Mauritian Attorney General Gavin Glover, who told the BBC in May: “Our country is elated that this 60-year struggle is finally over.”

However, two women born in Diego Garcia who wanted to be able to return there had raised a last-minute legal challenge against the deal in May.

The High Court went on to dismiss the challenge.