Investigators examined flight recorders yesterday from Russia's mystery double air crash in which 89 people died, but one official doubted they would be of any use.
"The tapes... did not show anything. Practically speaking they switched themselves off immediately. And so we failed to get any information," Vladimir Yakovlev, Russian President Vladimir Putin's envoy for the southern region, told ORT television.
Russian media focused on suspicion that the planes had been attacked within minutes of each other on Tuesday night, despite official statements that the crashes were most likely the result of technical fault or human error.
"Russia now has its own September 11," said a front-page headline in Nezavisimaya Gazeta daily, in reference to the 2001 suicide attacks on the US involving four hijacked commercial planes, which killed about 3,000 people.
One aircraft, a Tu-134 flying to Volgograd, went down south of Moscow. Moments later, a Tu-154 bound for Sochi on the Black Sea crashed near the southern city of Rostov-on-Don.
The planes had both left from Moscow's Domodedovo airport.
Investigators were deciphering flight recorders recovered from the wreckage but Mr Yakovlev said preliminary checks indicated they would not yield anything useful and indicated he believed a terrorist act was behind the disasters.
The source of Mr Yakovlev's information was unclear and Transport Minister Igor Levitin, heading the official investigating commission, said it was too early to pin down the causes.
"We have no clear idea today on what has happened. Not all the flight recorders are in a fit state to be read immediately. Experts will work on them today and tomorrow to make the tapes more acceptable for reading," he told NTV television.
Asked to comment on Mr Yakovlev's remarks, a spokesman for Mr Levitin said: "Yakovlev does not have any links with the commission."
A separate commission statement said the casing of a flight recorder from the Tu-134 had been slightly damaged and was being rebuilt by specialists to allow deciphering to take place.
Flags flew at half-mast and light entertainment shows were dropped from television out of respect for the victims as relatives went to the crash sites to identify their kin.
The crew of the Tu-154 hit the SOS button before their plane with 43 passengers and crew on board crashed, Mr Levitin said, "but there was no voice confirmation". Sibir Airlines, the owner of the Tu-154, previously said the pilots had triggered a hijack alert just before the crash.
The airline also said the fact that wreckage was scattered so widely indicated there may have been a mid-air explosion.
Prosecutor-General Vladimir Ustinov said he could not rule out a terrorist act or human and technical errors. But a spokesman for the FSB security service said initial investigations gave no evidence of a terrorist attack and focused more on possible faults with the planes or human error.
The incidents came against a backdrop of mounting violence in Chechnya, where Moscow has long been battling separatists.
Rebels launched a major raid in the regional capital last weekend and threatened more ahead of Sunday's presidential election. Moderate Chechen separatists deny any part in the crashes.