HOMS, Syria—Regime loyalists here voiced fury over a United Nations humanitarian relief mission for a rebel-held enclave in their city, accusing the organization of bias against minorities who support President Bashar al-Assad.

The U.N. said Monday that it was extending the relief mission for the old quarter of Homs for three more days. It has already evacuated more than 1,000 people and delivered desperately needed food while its convoys came under mortar and sniper fire on their way into the besieged enclave.

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