The worldwide trade in caviar was effectively suspended today when the UN said it could not approve export quotas for the expensive delicacy for the coming year.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) said that it was unable to set export quotas for the Caspian Sea basin, where 90 per cent of the world's caviar is produced, because it did not have enough information about the region's fish population and the illegal trade in the eggs.

Until a quota is set, Azerbaijan, Russia, Iran and Kazakhstan, the major exporters from the Caspian Sea basin, will be unable to sell the expensive sturgeon roe, which can cost as much as £5,000 per kg. Under CITES rules, roe harvested in one calendar year cannot be sold in the next, so 2005 stock can no longer be exported.

Announcing the news, Willem Wijnstekers, the Secretary-General of CITES, said that the UN had been preparing to set a low export quota for 2006 but was concerned that caviar exporters had not provided enough information about the full extent of the trade, both legal and illegal, in the eggs.

"Countries wishing to export sturgeon products from shared stocks must demonstrate that their proposed catch and export quotas reflect current population trends and are sustainable," said Mr Wijnstekers. "To do this they must also make full allowance for the amount of fish caught illegally."

Trade in caviar has been devastated in recent years by pollution, overfishing and poaching. As recently as the 1990s, the world trade in caviar, legal and illegal, exceeded 1,000 tonnes a year. Last year, the UN set a quota of just 105 tonnes for the Caspian Sea basin. Black market caviar is thought to account for about 100 tonnes a year. The trade is worth more than £100 million a year.

The finest caviar, known as Beluga and only found in sturgeon at least 24 years old, has become extraordinarily rare. In September, America, which consumes two thirds of the world's caviar, stopped importing Beluga caviar because the fish were so endangered.

Caviar traders said today's news reflected the parlous state of the world's most important population of sturgeon, but would not interrupt supplies. The harvesting season runs from late spring to late summer, so as long as CITES approves a quota within the coming months, no trade will be stopped.

"It's exactly what happened in 2001," said Gunther Costen of Princesse d'Isenbourg et Cie Ltd, a London-based caviar trader, referring to a temporary ban enforced by CITES four years ago. "It's just a temporary halt and then, of course, the quota will be curtailed again."

Mr Costen said it was wrong to call today's news a ban. "There is no possibility of catching the fish for several months," he said. "So people who are calling this a ban, I don't know what tree they are barking up."

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