Washington said the deal protected the long-term, secure and effective operation of the strategic military base.

After years of negotiations, the UK is giving up its sovereignty over a cluster of strategically important Indian Ocean islands. The move has led to criticism from Britain's Conservative opposition and some local Indigenous groups.

The UK will cede sovereignty of the Chagos Islands to Mauritius, but indigenous people from a tiny island that houses a US military base shrouded in secrecy will not be allowed to return