A hijacking signal was reportedly activated on one of two Russian passenger planes that crashed around the same time Tuesday night after leaving from the same Moscow airport.
The planes had 89 people on board. Russian President Vladimir Putin ordered an investigation by the nation's intelligence agency following the incidents. Security was tightened at the nation's airports as authorities said they were not ruling out terrorism.
A Tu-134 airliner carrying 35 passengers and a crew of eight was confirmed to have crashed in the Tula region, about 150 kilometres south of Moscow. A government spokesman said everyone on board was killed.
Three minutes after confirmation the first plane crashed, air traffic controllers lost contact with a Tu-154 jet carrying 38 passengers and eight crew members as it was flying near the city of Rostov-on-Don, about 1,000 kilometres south of Moscow, an official said.
Viktor Shkareda, the regional Emergency Situations Ministry chief, told the Associated Press that the plane apparently broke up in the air and that wreckage was spread over an area of some 40 to 50 kilometres.
The Russian news agency Interfax, citing an unidentified source, reported that the hijacking signal came at 11:04 p.m. from the Tu-154 airline
Both planes, which left from Moscow's Domodedovo airport 40 minutes apart, were medium-range Tupolev jets, one a three-engine model and the other with four engines.
ITAR-Tass news agency quoted an unnamed air traffic official in Moscow as saying authorities are not ruling out terrorism. The agency reported that witnesses saw an explosion before the crash in the Tula region.