Syrian rebels, frustrated by the West’s reluctance to provide arms, have found a supplier in an unlikely source: Sudan, a country that has been under international arms embargoes and maintains close ties with a stalwart backer of the Syrian government, Iran.

In deals that have not been publicly acknowledged, Western officials and Syrian rebels say, Sudan’s government sold Sudanese- and Chinese-made arms to Qatar, which arranged delivery through Turkey to the rebels.

The shipments included antiaircraft missiles and newly manufactured small-arms cartridges, which were seen on the battlefield in Syria — all of which have helped the rebels combat the Syrian government’s better-armed forces and loyalist militias.

Emerging evidence that Sudan has fed the secret arms pipeline to rebels adds to a growing body of knowledge about where the opposition to President Bashar al-Assad of Syria is getting its military equipment, often paid for by Qatar, the United Arab Emirates, Jordan, Saudi Arabia or other sympathetic donors.