At least 50 people were killed when a passenger plane crashed in central Russia on Sunday night, officials said.
The Boeing 737 from Moscow exploded after a failed attempt to land at the Kazan international airport, according to the Ministry of Emergency Situations in the Republic of Tatarstan.
Officials said that the plane had attempted to land several times prior to the crash.
The Tatarstan Emergency Situations Ministry said 44 passengers and 6 crew members were confirmed dead, but told Interfax News Service that as many as 52 could have been killed in the explosion.
Interfax also reported that the vice premiere of Tatarstan confirmed that Irek Minnikhanov, the son of the president of Tatarstan, and Alexander Antonov, the head of FSB (federal security service) of Tatarstan, died in the crash.
The crash was reported at 7:20 p.m. (10:20 a.m. EST), according to Interfax.
The flight was operated by the regional Tatarstan airline, a ministry spokeswoman told Reuters.
Flight U363 took off from Moscow's Domodedovo airport at 6:25 pm local time, and crashed just over an hour later, emergency officials said. The plane was 23 years old.
According to eyewitness reports to Reuters, the Boeing lost altitude quickly and its fuel tank exploded on impact.
There were high winds and cloudy skies over the airport in central Russia. Temperatures were above zero.
A spokesman for state aviation oversight agency Rosaviatsia said authorities wouldssearch for the flight recorders.
"The plane touched the ground and burst into flame," Sergei Izvolsky said. "The cause of the crash as of now is unknown."
In a statement, Boeing said, the company's "thoughts are with those affected by the crash ... [and] Boeing is prepared to provide technical assistance to the investigating authority as it investigates the accident."
Russia and the former Soviet republics combined had one of the world's worst air-traffic safety records in 2011, with a total accident rate almost three times the world average, according to the International Air Transport Association.
IATA said last year that global airline safety had improved but that accident rates had risen in Russia and the ex-Soviet Commonwealth of Independent States.
In April 2012, at least 31 people were killed when a Russian passenger plane crashed shortly after take-off in Siberia.
In September 2011, a Yak-42 passenger jet carrying members of a major league ice hockey team came down shortly after takeoff and burst into flames near the Russian city of Yaroslavl, killing 44 people.
The Boeing 737 is the world's most popular passenger jet in commercial use today. There have been 170 crashes involving this model of aircraft since it came into use.
In the Russian city of Perm in 2008, a Boeing 737 exploded just a kilometers above the ground minutes before landing, killing 88 people.
NBC News' Albina Kovalyova in Moscow and Reuters contributed to this report