A passenger plane plunged vertically when it crashed onto an airport runway in the Russian city of Kazan, killing all 50 people on board, Russia's transport minister says.
Investigators have found both of the flight recorders, or "black boxes".
The Boeing 737 was arriving from Moscow and trying to land, but exploded on impact at about 19:20 local time (15:20 GMT) on Sunday, officials said.
The Tatarstan Airlines jet had 44 passengers and six crew on board.
The crash happened as the 23-year-old plane was making a second attempt to land. Earlier that day it had flown to the Armenian capital Yerevan and back to Kazan, then to Moscow.
Investigators are examining several possible causes - a technical malfunction, pilot error or poor-quality fuel.
There are no suspicions that it was a terrorist attack.
It was raining at the time but the weather conditions were favourable for landing, officials say.
Citing witnesses of the crash, Russian Transport Minister Maxim Sokolov said "the plane was vertical, practically vertical, but the [video] recordings aren't very high-quality because it was dark".
The fuel tanks exploded on impact and it took hours to extinguish the blazing wreckage.
A spokeswoman for Tatarstan Airlines, Gulnaz Minnikhanova, said both pilots were very experienced and no technical problems had been reported with the plane before the flight.
The plane entered service in 1990 and had several previous owners, AFP news agency reports - Euralair Horizons (now defunct), Air France, Uganda Airlines, Brazil's Rio Sul, Romania's Blue Air and then Bulgaria Air.
While in Brazil it underwent a major repair after a non-fatal accident, AFP says.
Kazan is the capital of the oil-rich Russian Republic of Tatarstan, on the Volga River, about 720km (450 miles) east of Moscow.
Wide crash site
Irek Minnikhanov, a son of the Tatarstan president, was among the dead.
Alexander Antonov, who headed Tatarstan's branch of the Federal Security Service (FSB), was also among the passengers.
A top manager in Russia's anti-monopoly service, Rustam Guzhiyev, died too.
Two children were on board, and there were two foreign victims - a British teacher, Donna Bull from Cambridge, and a Ukrainian woman, Margarita Oshurkova.
Debris and bodies are scattered over a wide area and officials say DNA matches from relatives will be needed to identify charred remains.
Russian President Vladimir Putin "expressed his condolences to the relatives of the victims in this horrible disaster", his spokesman Dmitry Peskov was quoted by the news agency Interfax as saying.
A government commission has been set up to investigate the cause, he said.
The crew had said they were not ready to land because of technical problems, Russian news agencies report.
A journalist who said she had flown on the same aircraft from Kazan to Moscow earlier on Sunday told Russia's Channel One TV that there was a strong vibration during the landing in the Russian capital.
"When we were landing it was not clear whether there was a strong wind, although in Moscow the weather was fine, or some kind of technical trouble or problem with the flight," said Lenara Kashafutdinova.
"We were blown in different directions, the plane was tossed around. The man sitting next to me was white as a sheet."
The airport in Kazan has been closed since the accident.
Family members and friends of the victims are getting help from a team of psychologists. The government also promised financial compensation.
The BBC's Daniel Sandford in Moscow says that although some of Russia's biggest airlines now have very good reputations, frequent crashes by smaller operators mean the country has one of the worst air safety records in the world.