A Foreign Ministry statement in Moscow said: "The death of innocent civilians can only be a cause of deep outrage.

"We demand an immediate stop to Nato raids on Yugoslavia and stress the need to take immediate steps to facilitate a political solution in Kosovo," said the statement, issued as the Russian Foreign Minister met the US Secretary of State in Oslo.

In Beijing, the Foreign Ministry expressed "regret" at the bombing of the bridge, and urged Nato to stop its campaign "alleviate the humanitarian disaster" in Yugoslavia.

John Simpson in Belgrade: The worst error of the bombing so far

Nato admitted it had destroyed the train when it attacked a bridge 250km (155 miles) south-east of Belgrade. It said an investigation was under way.

Belgrade says the train became stuck near the town of Leskovac after an attack on a nearby road bridge severed its power lines.

Nato jets then returned and struck the railway bridge. Two carriages were reported to have burst into flames and another two were thrown from the track.

Rail officials said there were foreigners on board the train which was bound for Salonika, in Greece.

Nato said the railway bridge was a vital supply line for Serbian troops in Kosovo - but there was no intention of hitting the train.

Spokesman Jamie Shea said it was unclear whether the train was struck by a missile or destroyed when the bridge exploded.

"I want to stress very strongly indeed that there was no intention whatever to cause damage to the train,'' he added.

John Simpson in Belgrade: There do seem to have been some dreadful scenes

Journalists taken to the site near Leskovac six hours later said scattered body parts were strewn across the ground and there was a heavy smell of burned flesh.

"People were moaning, screaming for help," Tanjug quoted one of the rescuers, Dr Tomislav Cvetanovic, saying.

Dragan Ciric, 31, from Nis, said he scrambled through the window before his carriage became a ball of fire, Tanjug said.