Trucks destined for besieged areas in Syria are being loaded with humanitarian aid, part of an agreement between the Syrian government and the U.N.'s Syria envoy.

The Syrian foreign ministry hit back Wednesday against envoy Staffan de Mistura, who said the deliveries were a "test" of the Syrian government's commitment. A statement said "we do not wait for anyone to remind us of our duties toward our people."

Still, the convoys appeared to be preparing to head to besieged areas Wednesday.

The U.N. said the government of President Bashar Assad had approved access to seven besieged areas across the country and that convoys would head out in the coming days.

The U.N. estimates that 18 Syrian communities are besieged, affecting around half a million people.