The Kremlin covertly pre-positioned a fleet of attack aircraft in Syria in recent weeks, shipping in a fighting force for a possibly drawn-out air campaign, a leading Russian newspaper reported Thursday.

The fighter jets, bomber aircraft and helicopters are based at Khmeimi air base near the Syrian city of Latakia, the daily paper Kommersant reported, citing a source in Russia's military command.

It said the fleet includes Su-24M strike jets and at least six Su-34 bombers. Both aircraft are capable of carrying nuclear weapons.

There are also Su-25SM armored assault jets and at least four multipurpose Su-30SM fighter jets, according to the newspaper.

Other air assets deployed include Mi-24 attack and Mi-8 cargo helicopters, it said. All are from the Russian air force.

The newspaper said the aircraft were delivered unannounced while global attention was distracted by military exercises in Russia in mid-September.

The United States and other nations expressed concern around that time at the regular arrival of cargo planes in Syria that appeared to be from Russia, taking routes over Iran and Iraq.

The newspaper said the Russian ministry of defense has not revealed the number of military personnel currently in Syria who are taking part in the operation. It quoted Nikolai Bogdanovsky, deputy chief of the general staff, as merely saying no conscripts are currently serving outside Russia's borders.