MOSCOW (AP) — Russian strategic bombers struck targets in Syria Thursday in a third straight day of a heavy bombing blitz, military officials said.

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 of the Russian military General Staff 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.

Overall, Russian warplanes flew 126 combat sorties Wednesday, and on Thursday, more than 100 sorties are to be flown, Kartapolov said.

Early Thursday, the Tu-95 strategic bombers launched 12 long-range cruise missiles on IS targets, including its headquarters in the province of Idlib, fuel depots and a factory making explosives, he said.

A squadron of Tu-22M3 long-range bombers on Thursday struck six facilities in the provinces of Raqqa and Deir el Zour, hitting IS oil refineries, an ammunition depot and a facility manufacturing and repairing mortars, Kartapolov added.

He said earlier that Russian warplanes were focusing their strikes on the IS' oil production and refining facilities as well as oil trucks. He said that they destroyed about 500 trucks carrying oil in several days of strikes.

On Thursday, the chief of the Russian military General Staff, Gen. Valery Gerasimov, had a phone call with his French counterpart to discuss cooperation in the fight against the IS. The call followed Putin's order to the military to cooperate with the French "like with allies."

Gerasimov said the Paris attacks and the downing of the Russian plane in Egypt are "links of the same chain," adding that "our anger and our grief should help Russia and France unite their efforts in the fight against international terrorism."

French President Francois Hollande will visit Washington and Moscow next week for talks on pooling U.S., Russian and French efforts against IS.