The United Kingdom suffered a humiliating defeat Wednesday when the United Nations General Assembly overwhelmingly demanded that London cede to Mauritius the British-ruled Chagos Islands, home to an important military base.

The Indian Ocean archipelago has been at the center of a decades-long dispute over London’s decision to separate it from Mauritius in 1965 and establish a joint military base with the United States on Diego Garcia, the largest of the islands.

A total of 116 countries in the 193-nation assembly voted in favor of a non-binding resolution presented by African countries that urged Britain to “withdraw its colonial administration” from the Chagos Islands within six months.

The US, Hungary, Israel, Australia and the Maldives backed the UK in the vote and 56 countries abstained, including France, Germany, the Netherlands, Portugal, Poland and Romania. Other European allies including Austria, Greece, Ireland, Spain, Sweden and Switzerland voted for the UK to relinquish sovereignty.

The vote came three months after the International Court of Justice (ICJ) declared that Britain had illegally split the islands and should give up control of the Chagos.

After Britain ignored that ruling, Mauritius turned to the United Nations for help.

The resolution states that the United Nations and its agencies will recognize Mauritius’s sovereignty over the Chagos Islands and calls on all governments “not to recognize, support or abet the unlawful colonial administration” in the Chagos.

Resolutions adopted by the General Assembly are not legally binding, but they do carry political weight.

Given the concerted campaigning by the UK and the US to tip the vote in their favor, the scale of the defeat came as a surprise even to Mauritius.

“Even we didn’t expect support for the UK to go into single figures,” Jagdish Koonjul, the Mauritian ambassador to the UN, told the Guardian. “More importantly, this has happened despite the huge, huge, pressure on national capitals and at the UN.”

British diplomats said the non-binding resolution would have little practical impact. But it has taken a political toll, reducing support for the UK in the General Assembly and focusing dissatisfaction over its permanent seat on the UN Security Council. Britain lost its seat on the ICJ two years ago. Mauritius now intends to challenge UK membership of the Indian Ocean Tuna Commission.

Taking the UN podium, Britain argued that the dispute was a bilateral matter and stressed that it had opposed the move to seek the ICJ legal opinion.

British Ambassador Karen Pierce said the Diego Garcia military base “plays a vital role in keeping allies and friends – including Mauritius – in the region and beyond safe and secure.”

The United States has sent fighter jets from Diego Garcia to bomb Afghanistan and Iraq, and the facility was used as a CIA interrogation center after the 9/11 attacks.

In 2016, Britain renewed a lease agreement with Washington for the use of Diego Garcia until 2036.

– with reporting by AFP and The Guardian