The Gambia will be withdrawing from the Commonwealth, 48 years after joining.
No other reasons were given for the withdrawal which was announced on state TV.
Two years ago President Yahya Jammeh accused the UK of backing his political opposition ahead of elections. The UK said it would "very much regret" The Gambia leaving the Commonwealth.
There is a history of tension between President Jammeh, who came to power in a 1994 coup, and the UK.
Earlier this year, a Foreign Office report singled out The Gambia for its human rights record, citing cases of unlawful detentions, illegal closures of newspapers and discrimination against minority groups.
In August last year The Gambia was criticised by Amnesty International and others for executing nine prisoners by firing squad.
The Commonwealth was founded in 1931 but acquired its modern shape after 1949 as former British colonies and protectorates, including The Gambia, started to achieve self-government.