The U.N. humanitarian chief is urging the Syrian government to allow the delivery of aid to more than 2 million desperate people in hard-to-reach areas.

Mark Lowcock told the U.N. Security Council on Tuesday that the situation in Idlib, one of the opposition's last remaining footholds in Syria, is "alarming," with airstrikes, clashes between armed groups, overcrowding and severely stretched basic services.

He said the government asked the U.N. to provide assistance after it retook the former rebel-held Damascus suburbs of eastern Ghouta and released $16 million. But he said the U.N. has only received authorization to visit once since mid-March.

Lowcock reiterated the U.N.'s request to facilitate access, saying the government has approved a convoy to aid 70,000 people in Douma, but "facilitation letters have not been provided."