The incidents came against a backdrop of mounting violence in Chechnya, where Moscow has been battling separatists for a decade. Rebels launched a major raid in the local capital Grozny last week and have promised more attacks.
Moderate Chechen separatists denied any role in the crashes.
"Our government has nothing to do with terrorist attacks. Our attacks only target the military. This is part of the Russian propaganda plan to besmirch the struggle of the Chechen people," Farouq Tubulat, a spokesman for Chechen separatist leader Aslan Maskhadov, told Al Jazeera television.
The plane which crashed near Tula, operated by Volga-Aviaexpress, came down after nearly reaching its cruising altitude. The company said the plane was in good shape and its passengers had undergone all necessary security checks.
"I rule out pilot error, because even in the most serious conditions which can affect this kind of plane, such as loss of control or fire, the crew always has time to pass on information to the ground," Yuri Dmitriev, director of Volgograd airport, told Russia's First Channel television.
An Emergencies Ministry spokeswoman said there was no chance of anyone surviving as the plane fell from 10,000 metres (30,000 feet). Wreckage was spread over several kilometres (miles) with some pieces about the size of a car, TV footage showed.
Three minutes after the Volga-Aviaexpress Tu-134 crashed, air traffic controllers lost contact with the Sibir Tu-154. Its wreckage was not found until Wednesday morning.
Emergencies Minister Sergei Shoigu told Russian television that nearly all of the victims' bodies had been found, and flight recorders from both planes had been recovered.
He did not speculate on the causes of the crashes, but said Putin was being fully briefed on the crash investigation, informs Reuters. According to The Star when Russia's U.N. Ambassador Andrey Denisov was told of the initial report of two near-simultaneous crashes, he said, "Now we have to see if there's terrorism." In Washington, a U.S. official, speaking on condition of anonymity Tuesday evening, said it was the understanding of American officials that the two Russian planes disappeared within four minutes of each other, which "in and of itself is suspicious." President Vladimir Putin immediately put the country on full alert, tightened airport security and ordered the FSB - the successor to the KGB - to launch an investigation. Today agents were combing passenger lists for known terrorists and interviewing ground crew involved in both flights. Putin ordered the FSB to investigate both incidents "without delay", amid fears that Chechen terrorists or al Qaeda may be behind the attacks, informs This is London.
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It is assumed that the fighter will be created using new stealth technologies and have a very large interception range - up to 1,500 kilometers