Procedures for target selections are being changed, he said.

The Americans are making a concerted effort to placate China with public apologies from both the president and secretary of state, and an explanation from Mr Cohen.

Three journalists were killed in the attack

"While our initial investigation is still very preliminary in nature, in simple terms, one of our planes attacked the wrong target because the bombing instructions were based on an outdated map," said the defence secretary.

"The correct target was the federal directorate for supply and procurement, a key part of Yugoslavia's military machine."

Mr Cohen said the map on which the attack was based had been drawn up in 1992 with two updates, the last one in 1998.

These had shown the Chinese embassy to be at its previous location.

However, he said there was a mistake in identifying the building anyway. It was shown on the latest map but was unmarked, and was wrongly thought to be the procurement agency which is not far away.

"It was the right address applied to the wrong building," an intelligence official said, speaking on condition of anonymity. Another said, "None of the fail-safes worked."

Republican Senator Richard Shelby, who heads the Intelligence Committee, blamed the mistake on lack of resources.

It is "indicative of what happens when you ask too few people to do too much," he said.