By Imogen Foulkes
BBC News, Geneva
The UN has appealed to Indian Prime Minister Manmohan Singh to take action to save the Indian tiger.
Official estimates of tiger numbers are said to be an exaggeration
Willem Wijnstekers, head of the UN Convention on International Trade in Endangered Species (Cites), asked in an open letter for talks with Mr Singh.
India has more wild tigers than any other country, but Cites fears poachers are now rapidly reducing numbers.
It says it does not want to embarrass India but making the letter public is a last-ditch attempt to save the tigers.
Writing to India's prime minister is an unusual step and this letter is blunt.
But the UN body says the slowness with which India seems to be implementing anti-poaching measures could be seen as a lessening of its commitment to Cites - and India has signed the convention.
India's population of tigers in the wild is dwindling. Official estimates of around 3,500 animals are thought by conservationists to be an exaggeration.
And although it is 30 years since former Indian Prime Minister Indira Gandhi started Project Tiger to protect the species, numbers have not increased - rather the opposite.
Trade in tiger parts is banned worldwide but it continues.
Tiger skins are turning up in the apartments of Russian mafia bosses. Tiger bones are highly prized by Asia's gamblers.
John Seller, the chief enforcement officer of Cites, says poaching has become a highly professional operation.
He says networks of organised criminals gather skins and carcasses and smuggle them out of India using sophisticated techniques.
"If it is accurate that tigers have disappeared entirely from one of India's premier tiger reserves," he said, "then how [much] more serious can it get?"