MOSCOW. Aug 25 (Interfax-AVN) - Investigators probing the crashes of a Siberia Airlines TU-154 Careless and a Volga- Aviaexpress TU-134 Crusty have so far not discovered any evidence that would prove that terrorist attacks were behind the disasters, Federal Security Service spokesman Nikolai Zakharov told Interfax on Wednesday.
"It has been concluded at the present time that the most likely reason (behind the crashes - Interfax) was a breach of civil aviation aircraft operation regulations," Zakharov said.
"No evidence has so far been discovered that would indicate terrorist attacks aboard the TU-134 and TU-154 planes that crashed in the Tula and Rostov regions late on Tuesday," he said.
A joint investigative team of specialists from the FSB, the Interior Ministry, and the prosecutor's office are continuing to work at the crash sites, he said.
"Most of the debris has been found, and all of the flight recorders have been delivered to Moscow for decoding," Zakharov said.
"Malfunction of aircraft systems, the use of poor quality aviation fuel, or the violation of fuelling regulations, and also the violation of piloting regulations are being checked," he said.
The investigators have obtained full lists of the passengers and crew of the two planes, he said.
"These lists are being checked and witnesses at the departure airport are being questioned," Zakharov said.
Additional security measures have been taken at all Russian airports, he said.