The Russian military says its strategic bombers have struck targets in Syria in a third straight day of a heavy bombing blitz.

Russia, which has conducted air campaign in Syria since Sept. 30, sharply raised its intensity this week on President Vladimir Putin's orders.

Putin told the military to step up the bombing after the confirmation that the Russian plane crash in Egypt that killed all 224 people on board was downed by a bomb, which the Islamic State group said it had planted.

Col. Gen. Andrei Kartapolov said that long-range Tu-95, Tu-160 and Tu-22M3 bombers operating from Russian bases on Thursday took part in raids against IS targets in Syria. They joined Russian war planes based at the Hemeimeem air base in Syria's province of Latakia.