The first plane, a Tupelov-134 jet bound for Volgograd, crashed in the Tula region, near the village of Buchalki, some 200 kilometers south of Moscow. All 44 passengers, including nine crewmembers, were killed.
Some eyewitnesses say the plane exploded in the air before it crashed, but other reports cast doubt on this.
Russian Emergency Situations Minister Sergei Shoigu said today that, "regarding the Tu-134 near Tula, one of the flight recorders has been found in good condition and the search for the second flight recorder is ongoing and practically all the bodies of those who perished have been found."
ITAR-TASS later reported that all the flight and chart recorders from both planes have been found and brought to Moscow for investigation.
The small Volga-Aviaekspress airline, which owned the Tu-134, said all necessary security checks had been made prior to the flight. The company's director, Yurii Baichkin, was reportedly piloting the plane at the time of the crash.
Air-traffic controllers said they received no distress signals before the plane disappeared from their radars.
Minutes later, controllers also lost trace of a second plane, a Tu-154 carrying 46 passengers, including eight crewmembers. The plane, bound for the Black Sea resort town of Sochi, came down in the Rostov region, some 960 kilometers south of the capital.
Russia's Interfax news agency quoted a source saying the plane, owned by the Sibir air company, had sent out a hijack alert shortly before it disappeared. However, later the agency quoted an unnamed law enforcement official as saying the signal had been a general distress alert.
The Tu-154 wreckage was found about nine hours after the plane's disappearance. An Emergency Situations Ministry official in Rostov told AP that the plane apparently broke up in the air and that the wreckage was spread over some 40-50 kilometers. The fuselage and tail lay a few hundred meters apart at the edge of a forest.
The reasons for the crashes are still unknown. Sergei Ignatchenko, head spokesperson for the FSB intelligence agency, said today that the main scenario under investigation involves pilot or technical error:
"Several scenarios are being considered. The main scenario is violation of civil aircraft regulations," Ignatchenko said. "A terrorist act is also being considered as a possible cause, but there has been no evidence found up to this moment that it was a terrorist act."
The director of Volgograd International Airport, Yurii Dmitriev, told the journalists today he fully excludes pilot error as a reason for the crash.
"I exclude pilot error because even in the most difficult conditions arising in an aircraft of that type, such as a control malfunction or a fire on board the aircraft, crewmembers always have time to relay the information to [air-traffic controllers on] the ground," Dmitriev said.
There are fears the two planes may have been sabotaged by militants from the rebellious republic of Chechnya, which is due to elect a new president this weekend. Rebels have been blamed for a series of terror acts in Russia in recent years.
Akhmed Zakaev, a spokesman for Chechen separatist leader Aslan Maskhadov, said today that Maskhadov was not connected in any way to the simultaneous crashes.
A second spokesman, speaking to Al-Jazeera television, said the separatist government "has nothing to do with terrorist attacks. Our attacks only target the military."
In a recent interview with RFE/RL, Maskhadov had said he had reached an agreement with radical Chechen field commander Shamil Basaev that terrorist acts only harm the cause of Chechen resistance.