Non-Islamist opposition factions say they are using the US-made TOW missiles to halt a Syrian army advance that is backed by Russian air strikes in the provinces of Hama and Idlib.
The deliveries are distinct from ammunition packages that a US-led coalition airdropped to Arab rebel groups in northeastern Syria late Sunday to bolster the fight against the extremist Islamic State group.
"These rockets have played an important role in stopping the fierce attack by the Syrian regime and its Russian ally," said Asaad Hanna, spokesman for the non-Islamist Division 101.
According to the Syrian Observatory for Human Rights, non-Islamist groups in central Syria have been receiving increased amounts of TOWs in the past four days.
Observatory head Rami Abdel Rahman said that rebel commanders were telling their units to "attack any soldier you see using TOW missiles as we have a blank cheque" with supplies so plentiful.
In 2014, rebel groups vetted by the US received TOW missiles for use in the provinces of Idlib, Aleppo, and Latakia.