National Day Of Mourning In Russia

Russian officials are investigating whether terrorism caused Tuesday's near-simultaneous crashes of two passenger airplanes, killing all 89 people aboard.

The planes plunged just days before a Kremlin-called election in warring Chechnya, whose separatist rebels are blamed in a series of suicide bombings in recent years. Officials had expressed concern that Chechnya's separatist rebels, blamed for a series of suicide bombings in recent years, might try to carry out attacks ahead of the Sunday vote.

But officials say that no firm evidence of terrorism has yet been found in the planes' charred wreckage and they are looking into the possibilities of poor fuel and human error.

"Several versions are being examined, including a terrorist attack, and other possibilities - the human and technical factor," Russia's top prosecutor, Vladimir Ustinov, said during a televised meeting with President Vladimir Putin.

Putin didn't publicly address the terror question, choosing to instead focus on conveying his condolences to the families of the dead. He told investigators he wants "unbiased and reliable information" from the probe.

In addition to designating Thursday as a day of mourning, Putin ordered an investigation by the Federal Security Service (FSB) and security has been tightened at Russian airports and other transport hubs and public places.

The FSB says explosives experts are still sifting through the debris at the crash sites, and terrorism is still being considered as a possible cause.

In televised comments, FSB spokesman Sergei Ignatchenko said that the main scenario authorities are considering is a "violation of civilian aircraft rules," and that studies of wreckage at the crash sites have so far yielded no evidence of a terrorist attack. Officials are also considering defective equipment, human error, or substandard fuel as among the possible causes.

Officials have begun the job of extracting data from the flight data recorders or "black boxes" from the two planes, which were found in what officials described as satisfactory condition and brought to Moscow.

The planes - a Sibir airlines Tu-154 with 46 aboard and a Tu-134 with 43 passengers and crew belonging to tiny Volga-Aviaexpress airline - disappeared from radar around 11:00 p.m. Tuesday. The Tu-134 was headed to the southern city of Volgograd and the other plane to the Black Sea resort city of Sochi.

Both took off from the single terminal at Moscow's newly renovated Domodedovo airport, the Tu-154 around 9:35 p.m. and the smaller Tu-134 about 40 minutes later.

A spokesman for the Israeli Embassy said an Israeli citizen, David Coen, was on the Volgograd-bound jet, but the ITAR-Tass news agency said two Israelis were on the plane.

By early Wednesday morning, the wreckage of the Tu-134 had been discovered near the village of Buchalki about 125 miles south of Moscow. The plane lay upside-down in a large hay field, its tail severed from the fuselage.

Several hours later, searchers found the larger plane close to Gluboky, a village about 600 miles south of the capital.

Uncertainty over the cause of the crashes came after Sibir said that it was notified its jet had activated an emergency signal shortly before disappearing from radar screens. Officials said there were no indications of trouble with the other plane, but witnesses on the ground reported hearing a series of explosions.

Domodedovo airport said in a statement that both planes "went through the standard procedure of preparation for flight... (and) the procedures were carried out properly."

Still, there is skepticism that technical failure or human error could bring down two planes at almost the same time hundreds of miles apart. "That's pretty far out there on the chance bar," said Bob Francis, former vice chairman of the U.S. National Transportation Safety Board.

An aviation security expert, speaking with CBS News Correspondent Beth Knobel in Moscow, said he suspects terrorism.

"If it was only one accident, I would say a terrorist attack was possible. But two accidents? My God - it's hard to think of any other major likelihood of any reason,'' said expert Paul Duffy.

"The fact that the two accidents happening in Russia in one day is very, very extraordinary. The fact that they both happened coming out of the same airport within 45 minutes to each other is also very, very extraordinary,'' said Duffy.

Jim Burin of the U.S.-based Flight Safety Foundation said that although bad fuel could cause an airplane's engines to fail, the problems likely would be noticed and reported by the crew well in advance as the engines began to labor or misfire.

"I would expect some communication from the crew that we're having trouble," he said.

He added that initial reports from the crash scenes indicated that one plane's wreckage was spread out more widely than would usually be the case in a crash that was not preceded by an explosion.

Rafi Ron, former head of security at Israel's Ben Gurion Airport and now a security consultant in Washington, DC, said he is convinced this is a case of terrorism. "The timing indicates that this is probably a coordinated attack," Ron said.

"There was probably something on board that led the pilots to push the distress signal or submit a verbal signal," Ron said. "In my assumption, that must have been the result of a terrorist on board."

Chechen rebels and their supporters have made bold and brutal attacks both within the small southern republic and in Moscow - including the 2002 seizure of hundreds of hostages at a Moscow theater; several women in the raid were strapped with what appeared to be explosives. Officials also blame Chechens for suicide bombings, including one outside a hotel near Red Square and another at an outdoor rock concert in the capital last year.

If authorities connect the crashes to Chechen rebels, that would likely make the Kremlin even more adamant in its refusal to negotiate with the insurgents to end the war. But that also would underline Russia's inability to wipe out the rebels despite superior weaponry and manpower.