The Tu-154 crashed in eastern Ukraine en route from a Russian Black Sea resort to St. Petersburg, Russia's second biggest city. Pulkovo Airlines, which owned the plane, said Wednesday morning that 170 people - including 45 children under the age of 12 - had been killed. Other sources had suggested 171 passengers and crew had lost their lives.
"Both black boxes have been discovered," Svetlana Kryshtanovskaya said.
Experts are studying the flight data recorder, the first to be found, and the cockpit voice recorder in the hope of identifying why the tragedy happened.
A spokesperson for the emergencies services said Tuesday the plane had sent an SOS signal at 15:37 Moscow time [11.37 GMT] and vanished from the screens two minutes later. The St. Petersburg-based 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)
Preliminary reports that emerged Tuesday night suggested that the plane may have been struck by lightning.
A spokesman for Pulkovo Airlines, which until the tragedy had an excellent safety record, said earlier Wednesday that five foreigners - from the Netherlands, Germany, France and Finland - had lost their lives, according to preliminary information.
Although the Soviet-designed Tu-154 is known as a robust aircraft, Tuesday's tragedy was not the first in recent years.
In October 2001, Siberia Airline (now S-7) Tu-154 en route from Tel Aviv to Novosibirsk in Siberia was accidentally shot down by a Ukrainian S-200 missile, killing 78 people onboard.
In July 2001, another Tu-154 crashed near Irkutsk, claiming the lives of 145 people.
The loss in Ukraine was also the third major aircraft crash to have affected Russia this summer.
On July 9, an A-310 airbus owned by S-7 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.
