(CNN) The United Nations General Assembly has voted overwhelmingly to condemn the UK's continued occupation of the Chagos Islands -- a humiliating defeat for London on its continued colonial legacy.

The Indian Ocean islands, which are home to US military base Diego Garcia , were separated from the former British territory of Mauritius during decolonization in 1968. On Wednesday, UN member states voted 116-6 for a non-binding resolution endorsing a decision by the International Court of Justice (ICJ) that separation was illegal and calling for the UK to return the islands to Mauritius within six months.

Only Australia , Hungary, Israel, the Maldives and the US voted in support of the UK.

"The advisory opinion is clear and unambiguous," Mauritius Prime Minister Pravind Jugnauth said. "It is decisive."

Jugnauth said that decolonization of the former British Empire had not been completed, nor would it be until the Chagos Islands were returned to their original owners. "This is a sacrosanct principle of the United Nations," he added.

Karen Pierce, the UK's representative to the UN, said London "is not in doubt about our sovereignty over the British Indian Ocean Territory," which includes the Chagos Islands.

She said Mauritius had recognized British control over the Chagos archipelago in the past, something the current government has acknowledged but argues was done under "duress."

The entire Chagos Islands population was expelled and prevented from returning as part of the separation process, a situation the UK has since said "was shameful and wrong."

In the 1980s, the UK paid about $5.2 million to more than 1,300 evicted islanders on the condition they sign or place a thumbprint on a form renouncing their right to return to the archipelago.

"The detachment (or excision) of the Chagos Archipelago was carried out without any regard to the will of the people of Mauritius, including those who lived in the Chagos Archipelago," Mauritius said in a submission to the ICJ.

"The administering power had already decided that the territory would be excised and turned into a new colony, in order to allow one of its allies to build a military base on the island of Diego Garcia."

While the UN will not force the UK to give up the Chagos Islands, pressure is on for London to find a way to transition control to Mauritius. That may be compounded if a deal is worked out to maintain the US base under Mauritian rule.

Stephen Robert Allen, who specializes in international law relating to the Chagos Islands, told CNN ahead of the UN debate that "it will be a very significant thing if the UK decided to ignore such a ruling."

"As the UK forges a path post Brexit these political matters are going to be significant. Adhering to the international rule of law is going to be even more important than it would have been otherwise," he said.

Major US facility

Home to more than 1,000 US troops and staff, it has been used by the US Navy, US Air Force and even NASA. Diego Garcia has helped to launch two invasions of Iraq, served as a vital landing spot for bombers flying missions across Asia, including over the South China Sea, and has been linked to US rendition efforts.

According to the US Navy, Diego Garcia was used to guide tactical aircraft supporting military missions in Afghanistan and Iraq, and featured remote satellite tracking stations, an Air Force Space Command and Pacific Air Force support and logistics teams.

Carl Schuster, a former director of operations at the US Pacific Command's Joint Intelligence Center, said the base was "very important to US operations in the Persian Gulf and Indian Ocean" and its loss could have a major impact, forcing the US "to change logistics support" in the region.

"It wouldn't weaken (US military strength) necessarily, but logistics are everything," he added.