So far, no traces have been found in the other plane, but the investigation continues. It's possible it could've been brought down by other means. It's even possible that it was simply an accident, but the odds are against it.

Plane crash a terror attack: authorities

AT least one of the two Russian plane crashes that killed some 90 people this week was the result of a terrorist attack, the top Russian security service spokesman said.

"According to our initial investigation, at least one of the air crashes, the one in the Rostov region, came as a result of a terror attack," spokesman Sergei Ignatchenko told ITAR-TASS news agency.

Investigators said they had found traces of explosive material in the wreckage of one of the two planes that crashed in southern Russia, Russian news agencies reported.

"During the investigation of the wreckage of the Tupolev 154, we found traces of explosive material," a spokesman for the FSB intelligence agency was quoted by ITAR-TASS and Interfax news agencies as saying.

The spokesman, Sergei Ignachenko, identified the material as Hexogen, the same material that Russian authorities claimed was used in a series of apartment bombings in 1999 that killed some 200 people.

The plane in question was carrying 46 passengers and crew on a flight from Moscow to the Black Sea resort of Sochi.

It went down in the southern Russian region of Rostov, while another passenger plane carrying 43 people that had departed from the same Moscow airport crashed at almost precisely the same moment hundreds of kilometres further north.

The twin crashes raised immediate suspicisions of terrorism, possibly connected to controversial elections due this weekend in the war-torn Russian republic of Chechnya.