A Russian deputy foreign minister says that 160 Russians fighting for the Islamic State group have been killed in Syria.

Russian news agencies on Thursday quoted Oleg Syromolotov as saying that out of some 2,700 Russians fighting in Syria, 73 have returned and been convicted and 36 placed under arrest.

Russia in September began carrying out attacks on IS positions to support President Bashar Assad's forces. President Vladimir Putin on Tuesday pledged to intensify Russia's air operation there after the Russian intelligence chief announced that a bomb brought down a Russian plane over Egypt on Oct. 31, killing all 224 onboard.

IS claimed responsibility for the attack but Russians would not say whether they think the IS was behind it.