In recent weeks Russia has stepped up supplies of military gear to Syria, including armored vehicles, drones and guided bombs, boosting President Bashar al-Assad just as rebel infighting has weakened the insurgency against him, sources with knowledge of the deliveries say.

Moscow, which is trying to raise its diplomatic and economic influence in the Middle East, has been a major provider of conventional weapons to Syria, giving Assad crucial support during the three-year civil war and blocking wider Western attempts to punish him with sanctions for the use of force against civilians.

The new Russian supplies come at a critically fluid stage of the conflict, with peace talks scheduled for next week in Switzerland, the factious opposition losing ground, and Western support for the rebellion growing increasingly wary of the role played by foreign militants. Syria has even said some countries formally opposed to Assad have begun discussing security cooperation with his government. […]