The U.S. and its regional allies agreed to increase shipments of weapons and other supplies to help moderate Syrian rebels hold their ground and challenge the intervention of Russia and Iran on behalf of Syrian President Bashar al-Assad, U.S. officials and their counterparts in the region said.

The deliveries from the Central Intelligence Agency, Saudi Arabia and other allied spy services deepen the fight between the forces battling in Syria, despite President Barack Obama’s public pledge to not let the conflict become a U.S.-Russia proxy war.

U.S. officials said the Obama administration is pursuing what amounts to a dual-track strategy, which aims to maintain military pressure on Mr. Assad and his Russian and Iranian supporters while U.S. diplomats see if they can ease him from power through negotiations. U.S. officials said the pressure track was meant to complement the diplomatic track by giving the U.S. leverage at the negotiating table.