Russia's Federal Security Service said today that traces of explosives have been found in the wreckage of one of two airliners that crashed nearly simultaneously.
The statement came several hours after a website known for militant Muslim published a claim of responsibility for the crashes of two Russian airliners, connecting the action to Russia's fight against separatists in Chechnya.
A spokesman for the security agency, Nikolai Zakharov, said on Russian television that the traces were found in the shattered Tu-154 jetliner that crashed in southern Russia and that "preliminary analysis indicates it was hexogen."
Hexogen is the explosive that officials said was used in the 1999 apartment bombings that killed some 300 people in Russia and that were blamed on Chechen separatists.
Although authorities today stopped short of formally declaring the crashes as caused by terrorists, another Federal Security Agency spokesman, Sergei Ignatchenko, said authorities are trying "to determine the circle of people who may have been involved in an act of terrorism aboard the Tu-154," according to the Interfax news agency.
No results from the other crash site, of a Tu-134 about 200 kilometers (120 miles) south of Moscow, have been announced. At least 89 people were killed in the twin disasters.
Although the planes disappeared from radar screens within minutes of each other after taking off from the same airport, Moscow's Domodedovo, Russian officials had held back from declaring the crashes to be connected with terrorism, saying that other possibilities including bad fuel and human error were being investigated.
The prospect that explosives had been placed aboard two planes leaving from one of Russia's most modern and sophisticated airports was likely to raise serious concern about air security throughout the sprawling country.
There were no immediate indications that Russia was considering halting national air traffic, as the United States did after the Sept. 11 attacks. A duty officer at Sheremetyevo airport in Moscow said all flights were taking off and landing as scheduled.
The crashes took place just five days before presidential elections were to be held in Chechnya, where rebels and Russian forces have been fighting for nearly five years. Officials had warned of concern that separatists could try to commit attacks ahead of the elections, which are to fill the post of the late Kremlin-backed Chechen president Akhmad Kadyrov, who was assassinated by a bomb in May.
The statement of responsibility published on the militant Muslim Web site was signed "the Islambouli Brigades." A group with a similar name has claimed responsibility for at least one other attack, but the authenticity of Friday's statement could not immediately be confirmed.
Russian officials have repeatedly contended that the rebels who have been fighting Russian forces in Chechnya for nearly five years receive help from foreign terrorist organizations, including al-Qaida.
Friday's claim did not refer to al-Qaida, but a group called "the Islambouli Brigades of al-Qaida" claimed responsibility for last month's attempt to assassinate Pakistan's prime minister-designate.
The statement did not give details on how the alleged attacks on the Russian planes occurred. The planes went down within minutes of each other after both had taken off from Moscow's Domodedovo airport.
"Our mujahedeen, with God's grace, succeeded in directing the first blow which will be followed by a series of other operations in a wave to extend support and victory to our Muslim brothers in Chechnya and other Muslim areas which suffer from Russian faithlessness," the statement said.
It was not clear whether the statement claimed that Chechens themselves staged attacks on the planes.
However, Russian news agencies reported Friday that investigators were searching for information about two women with Chechen surnames who were on the planes' passenger lists. They are the only passengers about whom relatives have not inquired, the reports said.
Chechen rebels and their supporters are blamed for a series of suicide bombings and other attacks in Chechnya and the rest of Russia over the past several years, including last year's suicide bombings of an outdoor rock concert in Moscow and another outside a hotel near Red Square.
The crashes took place just five days before Chechens were to vote for the republic's president, to replace Kremlin-backed Chechen president Akhmad Kadyrov who was assassinated in a May 9 bomb attack.
Officials had warned that Chechen separatists might try to carry out attacks ahead of the vote, which is part of the Kremlin's strategy of trying to undermine the insurgents by establishing a modicum of civil order in the region.
Security analyst Andrei Soldatov said the reported Chechen connection could bring more suffering to the republic, where Russian forces are widely criticized for abusing and abducting civilians.
"The government will now be able to say that the fight against separatists in Chechnya comes under the roof of international terrorism. As soon as they say that, you can forget about human rights in the region," he said.