Arab nations and Turkey, helped by the CIA, have dramatically increased military aid to Syrian rebels in recent months, The New York Times reported Monday.
The US Central Intelligence Agency was helping their efforts, the newspaper added, citing air traffic data and interviews with unnamed officials and the rebel commanders.
The airlift has grown to include more than 160 military cargo flights by Jordanian, Saudi and Qatari military-style cargo planes landing at Esenboga Airport near Ankara, and at other Turkish and Jordanian airports, the report said.
US intelligence officers have helped the Arab governments shop for weapons, including a large procurement from Croatia, it said. They had also vetted rebel commanders and groups to determine who should receive the weapons as they arrive.
Turkey had overseen much of the program, fixing transponders to trucks ferrying the military goods through Turkey so it could monitor shipments, the paper added.
"A conservative estimate of the payload of these flights would be 3,500 tons of military equipment," Hugh Griffiths, of the Stockholm International Peace Research Institute (SIPRI), told the paper.
"The intensity and frequency of these flights," were "suggestive of a well-planned and coordinated clandestine military logistics operation", he added.
The armed uprising against the government of Syrian President Bashar al-Assad sprang up in response to the Damascus regime's crackdown two years ago on opposition protests.