MOSCOW - Russia’s law-enforcement agencies have reacted swiftly to the Tuesday’s night plane crashes by tightening security at all airports in the country as they opened criminal investigations into the crash incidents. The move stemmed from the authorities' belief that the deadly acts could have been masterminded by terrorists.

"There are solid grounds for opening a criminal case under this article of the Criminal Code, because a minute before the plane's crash, the Rostov police office department had received a message from air traffic controller Sviridov, who said the plane's crew had been attacked," an unidentified source in the Rostov regional prosecutor's office said, according to Interfax.

Other aviation experts share the same view: "The fact that both planes took off from one airport and disappeared from radars around the same time . . . shows the incidents could have been planned in advance," a Russian aviation-security expert told Interfax.

President Vladimir Putin has been informed of the incidents, and he has ordered the Federal Security Service (FSB) to launch a probe into the air disasters, presidential spokesman Alexei Gromov told Interfax. “Putin is being regularly informed about the situation by officials of the Emergency Situations Ministry, the FSB and other law enforcement agencies.”

Currently, the FSB and police are examining the lists of passengers and questioning the personnel who prepared the planes for the flight at the Domodedovo airport, from which the two ill-fated planes took off to Volgograd and Sochi on Tuesday. The airliners, a Tu-134, owned by Volga-Avia Express, was en-route to Volgograd, while Tu-154, owned by Siberia Airlines, was on its way to Sochi, a resort city in southern Russia when the blasts occurred almost simultaneously at about 11pm Tuesday in different parts of the country several minutes after taking off the airport. Some parts of the Tu-134’s remains were later discovered in the Tula Oblast, while Tu-154’s debris was discovered in the Rostov region. Both planes’ crewmembers and passengers are feared dead, according to official sources.

The exact number of passengers and crewmembers on both planes has yet to be determined, with the calculations being worsened by state aviation and airline officials’ conflicting figures. For instance, the Interstate Aviation Committee, the official regulator in the civil aviation industry, said there were 34 passengers and eight crewmembers aboard the Tu-134 and 44 passengers and on the Tu-154, while Siberia Airlines, the owner of Tu-154, said there were 38 passengers and eight crewmembers on the Tu-154.

The Emergency Situations Ministry, which is handling the search-and-rescue operations, has a totally different set of figures. On its last counts, the ministry put the number of passengers and crewmembers on the Tu-134, respectively at 35 and eight, and for the Tu-154, respectively at 38 passengers and eight.