Aid workers trying to deliver humanitarian supplies to the besieged, rebel-held district of Homs, were wounded on Saturday after reportedly coming under fire from "armed terrorist groups," the label authorities give to rebels fighting President Bashar al-Assad.

Four Syrian Arab Red Crescent workers were hurt in the reported attack, according to Syrian state television. Opposition groups did not immediately respond to the allegations.

As NPR's Alice Fordham reports, it's the latest sign that a hard-won ceasefire is fraying.

The Red Crescent, which posted the picture shown above on its Twitter feed, said the vehicle driver was among the wounded. Other reports said four were hurt.

The plan for aid to enter the area is part of a deal struck between the government and rebel forces, with the idea that women, children and the elderly who wanted to leave, could be evacuated. Food and medicine is meant to come in for those who want to stay.

The Associated Press reports that the humanitarian convoy had been delayed since Saturday morning by mortar fire in Homs. It said that Syrian television quoted the governor of Homs, Talal al-Barazi, as saying two cars carrying aid supplies had entered the Old City but that rebels had targeted the route with mortar fire, preventing any more vehicles from entering."

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