As Russia continues airstrikes in Syria, officials in Moscow have sent missile defense systems to the region as a precautionary measure against any threats, including possible hijacking of their air force planes. Russia claims that its airstrikes are aimed at the Islamic State group and were started at the request of Syrian President Bashar Assad, but U.S. and other Western countries, who have been calling for Assad to step down, believe the strikes are aimed at protecting the Syrian ruler.

“We have taken into account all possible threats. We have sent not only fighters, attack aircraft, bombers, and helicopters, but also missile defense systems because any sort of force majeure situation may occur. For example, the stealing of a warplane in a neighboring country with Syria or having to return fire. We need to be prepared for that,” Russian Aerospace Forces Commander Viktor Bondarev said, according to Russia’s state-run news agency Sputnik News.

The latest comments from Bondarev follow claims by an Egyptian affiliate to ISIS, Sinai Province, this week that they brought down a Russian passenger plane in Egypt’s Sinai Peninsula on Saturday, killing all 224 people on board. The group said that it targeted the Metrojet plane to retaliate against the Russian airstrikes.

Russia announced it would conduct airstrikes in Syria in September. On Tuesday, the country’s defense ministry said that the Russian air force has so far flown 1,631 sorties and struck 2,084 militant targets since beginning of the operation. On the same day, the U.S. and Russia also held a joint training exercise in Syria as a part of an effort to share intelligence and cooperate to tackle militant organizations in the region.

"There was a joint exercise with air crews and ground troops from the Russian and U.S. air forces," Russian General Andrei Kartapolov said, according to Reuters. He added that the training involved Russian and coalition jets practicing close encounters in a special zone, at a minimum distance of three aeronautical miles.