The Tu-154 jet owned by St. Petersburg-based Pulkovo Airlines was flying from the Russian resort of Anapa on the Black Sea to St. Petersburg via Ukrainian territory and crashed 45 kilometers (30 miles) outside Donetsk in eastern Ukraine near the Russian border.
"The plane was caught in a thunderstorm and hit by a lightning strike," the emergency services said. "The Tu-154 jet fell from an altitude of 10-11,000 meters [about 33,000 feet]."
Ukraine's Emergency Situations Ministry said the airliner had asked to make an emergency landing.
"The airliner asked to make an emergency landing, but disappeared from radars at 2:30 p.m. [local time] (3:30 p.m. Moscow time, 11:30 a.m. GMT)," the ministry said.
Pulkovo Airlines, which had an excellent safety record prior to Tuesday's tragedy, said 39 children under the age of 12 and six under the age of two had been among the passengers.
An emergencies official in St. Petersburg said Dutch nationals were onboard, adding their exact number had yet to be clarified.
The airline said the plane, built in 1992, was in good working order and the pilot was experienced, with over 9,000 flying hours under his belt.
Stormy weather has been considered the main cause of the accident from the beginning as emergency services moved immediately to quell fears that terrorists could have targeted the Tu-154, the mainstay of the Russian air fleet.
"A terrorist attack is ruled out," Irina Andrianova said. "Ukrainian sources said the plane was caught in a thunderstorm."
Russian television's Channel One said, citing Ukrainian sources, said that the plane had caught fire at an altitude of about 33,000 feet (10,000 meters) and the crew had decided to make an emergency landing after sending an SOS signal.
A spokesperson for the emergency services told Russian television channel RTR that the plane gave an SOS signal at 15:37 Moscow time [11.37 GMT] and vanished from radar screens two minutes later. The airline said the crew had sent four mayday signals before contact was lost, three at 38,600 feet (11,700 meters) and one two minutes later at 10,000 ft (3,000 meters)
The plane was expected to land in St. Petersburg, where doctors and psychologists are now attending to distraught relatives of the passengers, at 17:45 local time (13:45 GMT).
Eyewitnesses told Russia's NTV television channel that the plane was intact when it hit the ground. Others suggested the jet had failed to lower its landing gear.
Human negligence also remains a focus of investigations, as the Prosecutor General's Office said it had launched an inquiry into possible violations of air traffic rules.
Ukrainian emergency services, prosecutors, and medical crews are working at the scene saying bad weather has complicated what has already become a recovery rather than a rescue effort.
A spokeswoman for the Russian Emergency Situations Ministry said the recovery operation would continue into the night, and that firefighters at the scene had almost tackled the blaze, which had been hampering the effort.
"The fire has virtually been extinguished," Irina Andrianova said. "Rescuers are recovering the bodies." So far 30 bodies have been recovered from the three-engine plane.
The spokeswoman added that three Russian helicopters were preparing to fly to the scene.
The Kremlin press office reported that Ukraine's President Viktor Yushchenko expressed condolences to his Russian counterpart over the air crash and pledged full assistance in investigations.
"Yushchenko said Ukrainian authorities would provide aid to the relatives and friends of those killed, and assistance in investigating the accident," the Kremlin said.
The local authorities at the crash site have set up a center to keep the relatives updated on progress of the investigation. The Donetsk Region's authorities said the list of the passengers onboard was still being clarified.
Series of accidents
President Putin has been informed about the accident and has ordered Prime Minister Mikhail Fradkov to set up a commission into crash. Russian rescuers are also on standby to fly to the area.
The tragic incident is one in a series of Russian crashes in the past few years.
On July 9, an A-310 airbus owned by S7 Airlines crashed killing 124 people on the way from Moscow to Irkutsk, the home airport for popular tourist destination Lake Baikal in Siberia. It veered off the runway upon landing and caught fire after hitting a concrete wall and plowing into garages.
On May 3, another Airbus operated by Armenian carrier Armavia crashed as it was preparing to land at the airport of Adler, off Russia's Black Sea coast. All 113 passengers and crew died.
In October 2001, a Siberia Airline (now S7) Tu-154 en route from Tel Aviv to Novosibirsk in Siberia was accidentally shot down by a Ukrainian missile S-200, killing 78 people onboard.
In July 2001, another Tu-154 crashed near Irkutsk, claiming the lives of 145 people.