The announcement came hours after a militant Muslim group claimed responsibility for two nearly simultaneous airplane crashes that killed 90 people Tuesday.
Nikolai Zakharov, a spokesman for the Federal Security Service, told Russian television that an explosive had been found and "preliminary analysis indicates it was hexogen," the Guardian reported.
Hexogen, more widely known as RDX, is a powder that when mixed with TNT is used as an explosive element in artillery shells and torpedoes, according to Reuters.
The traces of explosives were found in the wreckage of the Tu-154 aircraft that crashed in southern Russia shortly after taking off from Moscow's Domodedovo airport, killing 46 people. A Tu-134, departing from the same airport with 44 people aboard, crashed just minutes earlier.
Investigators said the crew of the Tu-154 had activated a distress signal right before crashing, but failed to provide voice confirmation, Reuters reported.
At first, Russian officials were reluctant to connect the events to terrorism, citing bad fuel and human error as other possible causes. But Russian presidential envoy for the region that includes Chechnya, Vladimir Yakovlev, said Thursday that terrorism was the most likely cause.
The crashes come just ahead of Sunday's scheduled presidential elections in Chechnya, where rebels and Russian forces have been fighting for nearly five years. Officials had warned of possible attacks by separatists ahead of the election, which is trying to fill the post of the late Kremlin-backed Chechen president Akhmad Kadyrov, who was assassinated by a bomb in May.
Moderate Chechen separatists denied any part in the crashes.
Russian officials said the same explosive found in the airplane wreckage was used in the 1999 apartment bombings that killed 300 people in Russia, an attack blamed on Chechen separatists, according to the Associated Press.
Chechen rebels and their supporters have been blamed for a series of suicide bombings and other attacks in Chechnya and the rest of Russia over the past few years. Russian officials contend that the rebels receive help from foreign terrorist organizations such as al-Qaida.
A Web site connected to Islamist militants published a statement signed by the "Islambouli Brigades" took responsibility for the crashes. The authenticity of the statement could not be immediately confirmed.
The statement said five "mujahedeen" or holy fighters were aboard each plane.
"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.
The Web site did not refer to al-Qaida, but a group called the "Islambouli Brigades of al-Qaida" has claimed responsibility for last month's attempt to assassinate Pakistan's prime minister-designate.
Russian officials said they were investigating two female passengers -- one on each plane -- with Chechen names, who were the only ones whose relatives did not contact authorities, the AP reported.
Paul Duffy, a Moscow-based aviation expert, told Associated Press Television that he found it "hard to believe" that five attackers were aboard each plane, "but there is no doubt that they had one at least on each aircraft."