Two passenger jets crashed simultaneously in different places after taking off from the same Moscow airport, leaving 89 people dead and raising fears anew Wednesday of terrorism in the heart of Russia.
Russian emergency workers comb the fields searching for bodies
The planes departed within about an hour of each other late Tuesday bound for destinations in southern Russia and went down at almost precisely the same moment 770 kilometers (480 miles) apart in two regions south of the Russian capital.
Wreckage and bodies lay strewn across fields outside the central city of Tula and the southern city of Rostov-on-Don as hundreds of emergency workers used cranes to sift through the detritus and extract corpses.
Officials were at a loss to explain how the planes went down with such improbably coincidental timing and said the possibility that the crashes resulted from terrorist attacks was being "carefully studied" along with other theories.
There were however no claims of responsibility for the twin disasters and investigators also indicated that they were looking at other possible explanations including bad weather, pilot error and problems with the fuel pumped into the jets.
"The hypothesis of a terrorist act is being carefully studied" by experts from the FSB intelligence service and other government agencies, FSB spokesman Sergei Ignachenko told AFP.
Russian security agencies were already on heightened alert ahead of elections Sunday in the war-torn republic of Chechnya that some breakaway rebel groups have vowed to thwart with violence if needed.
Putin: We will investigate without delay
President Vladimir Putin, in a statement transmitted by Russian media, ordered security agencies to investigate the crashes "without delay" but there was little official comment on the crashes apart from death toll updates.
Russian media reported that the planes were carrying a total of 90 passengers and crew. That figure however was later revised to 89 after authorities published figures indicating one plane had 46 people aboard and the other 43.
Grief-stricken relatives and friends of the passengers on the plane converged on Domodedovo airport where authorities said they would provide information updates and psychological assistance.
The "black box" flight data recorders from both aircraft were recovered and Russian news agencies reported that one of the planes had issued a distress signal before plummeting to the ground.
Russian Emergency Ministry soldier inspects debris of Russian Tu-134, which crushed near the village of Buchalki in the Tula region early Wednesday morning.
AFP reporters at the crash site outside Tula spoke to witnesses who claimed to have heard an explosion as the plane passed over the city, but their accounts offered little in the way of explaining how the plane went down.
Meanwhile, authorities in Moscow announced that precautionary steps were being taken to tighten security at the city's airports and other public sites with the participation of the FSB and other government agencies.
"All of the security services have been instructed to step up their vigilance," Moscow government spokesman Kirill Mazulin said, according to Interfax news agency.
An increased presence of police officers and other security personnel in public transportation stations and around many government buildings had already been in evidence over the past week.
A number of large public events, including a "Moscow City Day" celebration, were scheduled to be held in the capital in the coming days and security forces were carrying out frequent spot identification checks of people on the streets.
The heightened security in the capital and elsewhere reflected official concern that the vote in Chechnya, an election the Kremlin seeks to hold up as a sign of democratic progress in the embattled republic, not be disrupted in any way.
Chechen rebel denies attack on airliners
One key Chechen separatist leader, Aslan Maskhadov, has claimed responsibility for recent attacks on Russian soil and has vowed to sustain violent opposition to Moscow's political objectives for Chechnya.
A spokesman for Maskhadov however flatly denied the rebel leader had any connection to the plane crashes.
Chechen rebels or their supporters have been blamed for two major bomb attacks in Moscow this year, one that occurred in the subway during morning rush hour and another on a busy public sidewalk across the street from the Kremlin walls.
On Tuesday, four people were injured in a bomb blast at a bus station on the outskirts of Moscow. No one has claimed responsibility for that blast.
Meanwhile, emergency personnel said they had recovered dozens of bodies at both crash sites and were transporting remains to local morgues.
The Interfax news agency said debris from the plane that hit the ground near Rostov was scattered over fields and forests along a 10-kilometer (6.2-mile) trajectory.