Russia said Friday terrorists were behind at least one passenger jet crash, as an Islamic group vowing support for Chechen rebels claimed responsibility for that attack and destruction of another airliner.

Russia's Federal Security Service (FSB) said they had found traces of explosive materials in the wreckage of one of the two Russian planes, which crashed almost simultaneously Tuesday night after taking off from Moscow's airport.

A spokesman for the Service identified the materials as hexogen.

Russia's Interfax news agency quoted an unnamed official from the Chechen Interior Ministry as saying that a Chechen woman was a passenger on the crashed Tu-154.

Earlier reports have said she was the only passenger on the crashed flight who had not been asked about by relatives.

The Islamic group, calling itself the Islambouli Brigades, linked the crashes to events in Chechnya and hailed the downing of both planes as a first strike to stop Moscow's fight against separatists in Chechnya.