"I know you never liked me Mr. Secretary-General – well, I never liked you, either," said Mr Sha as Mr Ban looked on, smiling and nodding awkwardly during the 15-minute toast attended by the UN's top brass.

Mr Sha, who was appointed the UN undersecretary general for Economic and Social Affairs in 2007, also made no secret of his fractious relationship with Mr Ban, although did say he'd grown to respect the South Korean.

"You've been trying to get rid of me," said 62-year-old Mr Sha according to the senior UN official present, "You can fire me anytime, you can fire me today."

Later in his impromptu speech Mr Sha turned to an American colleague, singling out Bob Orr, from the executive office of the secretary-general.

"I really don't like him: he's an American and I really don't like Americans," he said.

A second senior UN official who was at the dinner said: "It went on for about ten or fifteen minutes but it felt like an hour."

Officials present at the dinner suggested that Mr Sha might have been the victim of a misguided attempt at humour.

The next morning Mr Sha requested a meeting with Mr Ban during which he was "deeply apologetic" according to Farhan Haq, the acting deputy UN spokesman.

Mr Farhan said: "Mr Sha told the Secretary General that he realised that the way that he spoke, coming as it did after he had had a few drinks, was inappropriate, as it went too far. He was also aware that his statements had embarrassed and irritated other senior advisers."

It is not the first time that Mr Sha, a career diplomat, has let the mask of diplomacy slip. In a BBC interview in 2006 he was goaded into a furious, shrieking attack on American criticisms of China's rapidly growing defence budget.

"It is much better for [America] to shut up, keep quiet. Are you the number one? Is it true that the US has almost 50 per cent of the world's military budget?"

The Chinese population is five or six times bigger.

"Why blame China? Forget it. It's high time to shut up. It's America's sovereign right to do whatever is good for them. But don't tell us what is good for China."