UEBERLINGEN, Germany -- Scores of Russian children heading for the holiday of their lives died when their plane collided with a cargo jet, leaving the German resort of Lake Constance strewn with bodies and burning debris.

Officials said 71 people, including 52 children and teenagers, were killed in the Monday night crash between a Bashkirian Airlines jet bound for Barcelona, Spain, and a Boeing 757 cargo jet operated by the International Courier Company DHL.

Witnesses said they heard rolling thunder and saw an orange glow and fireballs resembling comets in the night sky. A black rain of wreckage then poured down on the northern shore of this lake in southwestern Germany, AFP reported.

There were 69 Russians on board the seven-year-old Tupolev 154 airliner and a crew of two, a Briton and a Canadian, on the Boeing bound for Brussels.

The collision prompted western experts to question the safety commitment of Russian airlines, though a Russian Airline official denied the Tupolev crew had made any mistakes.

Swiss air traffic controllers, in charge of Lake Constance airspace because it is close to Switzerland, said the Tupolev reacted too slowly to orders to lower its altitude.

German air traffic investigators said the message traffic between Swiss controllers and the Russian plane showed the Tupolev pilot did not react to a first warning to lower his altitude to avoid the Boeing.

He responded to a second warning and began to descend 25 seconds before the crash, the Air Accident Investigation Authority BFU said.

But then the Boeing also began to descend, responding to its own onboard collision avoidance system. The BFU said it was still checking why the Boeing's system told it to descend.

Russian Prime Minister Mikhail Kasyanov described the collision as a "terrible tragedy" and said the cause was a mystery. "The scope of this tragedy is beyond understanding," he said after meeting French President Jacques Chirac in Paris.

Chancellor Gerhard Schroeder sent his "heartfelt condolences" to Russian President Vladimir Putin, and Pope John Paul said the victims would be in his prayers.

Eyewitnesses described how the collision turned this region of chocolate-box beauty into a scene from hell in seconds. There were no casualties on the ground even though police said they found pieces of wreckage in 57 different places.

"We came across five bodies just lying in the field next to each other," said Wolfgang Steiner, gardener at a children's home just 200 meters (yards) from where the tail section of the Tupolev came crashing down.

"One had his neck broken, one was missing a foot but there was no blood. I kept saying to myself, why is there no blood? They were adults, but they looked so small lying in that field." One television journalist described families staring white-faced with shock at pieces of burning wreckage in their gardens. Reuters' Television showed body parts covered by black plastic sheeting.