image sourceGetty Imagesimage captionStamps marked British Indian Ocean Territory now won't be recognised

Mauritius has moved a symbolic step closer to wresting control of the Chagos Islands, in the Indian Ocean, from the UK.

The Universal Postal Union (UPU), a UN agency in charge of the world's postal policies, voted to block the use of UK stamps from the remote archipelago.

All post to and from the Chagos Islands must now bear stamps from Mauritius.

The UK says it will not cede control until the islands are no longer needed for security purposes.

The US currently uses the largest of the islands – Diego Garcia – for a military air base on what the UK describes as the British Indian Ocean Territory (BIOT).

Three powerful UN bodies have already ruled that the archipelago, which has a population of about 3,000, is part of Britain's old empire and should be handed to Mauritius immediately.

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A set of pretty postal stamps showing sea slugs and angel fish might not seem like the sharp end of international diplomacy, the BBC's Africa correspondent Andrew Harding says.

But he adds that the near unanimous vote by the UPU to make those stamps illegal worldwide, is a blow to Britain, and another sign of its growing isolation over its claim to the Chagos Islands.

The next step could see Mauritius seeking to ban international flights over the area – a vast chunk of the Indian Ocean.

All indications so far show that on the Chagos issue – Britain has almost no allies left, our correspondent says.