The troops were returning home from duty in Kosovo when the Antonov plane crashed and exploded into flames near the village of Telkibanya, spewing body parts and bits of metal around the freezing terrain.

One person apparently survived, although it was not clear if it was a man who was able briefly to call his wife on a mobile phone before the line went dead.

"There are 42 dead and a sole survivor," said Tibor Dobson, who heads the Hungarian interior ministry's disaster prevention unit, by telephone from the crash site near Telkibanya.

The survivor was rushed in critical condition to a hospital in Kosice, on the Slovakian side of the border.

The death toll was confirmed by Slovakian Prime Minister Mikulas Dzurinda who said his government would declare a national state of mourning.

He refused to speculate on the cause of the accident but Hungarian Defence Minister Ferenc Juhasz told reporters in Budapest it was due to a "navigation error."

He said an investigation was being carried out by Hungarian civil aviation authorities.

On Thursday evening, Michaela Farkasova, the wife of one of the soldiers on board, told the Slovak channel TV3 that her husband contacted her immediately after the crash at around 7:30 pm (1830 GMT).

"He told me that the aircraft had crashed and was on fire and was somewhere in the forest. He told me that he was alive and to alert the rescue services and police. Then the line went dead," she said.

A source close to the Slovakian military told AFP that "the plane crashed into a mountain" while flying at about 700 metres (2100 feet), before bursting into flames.

The "black box" registering flight details from the Antonov plane had not yet been found, the Hungarian press agency MTI said.

The 43 people on board included seven crew members.

Body parts were scattered around the site, making it difficult to count and identify the head, Dobson said. "We are trying to piece together the bodies of the victims which were scattered over a very large area. It is very grim," he said.