A leader of U.N.-backed humanitarian efforts for Syria says he's "disappointed" with recent efforts to get aid convoys into hard-to-reach and besieged areas, and is calling on the government to "live up to its promises."

Jan Egeland, the humanitarian aid adviser for the U.N.'s Syria envoy, told reporters Thursday in Geneva that "April was supposed to be our best month" but that aid delivery is "not getting better and better, it's actually slowing down."

Egeland spoke during a break in U.N.-sponsored indirect talks between the Syrian government and the opposition delegation, which are to resume next week

Humanitarian assistance to Syria's people is part of an international response to the country's crisis that also includes a U.S.- and Russia-monitored cease-fire that has largely held over the last month.