The humanitarian situation in Syria is worsening rapidly with some areas a landscape of "devastation and destruction", the Red Cross said on Thursday after a month which activists said was the bloodiest yet in the conflict.
About 70,000 people have been killed and millions displaced during the two-year-old uprising, the United Nations says.
Civilians have been cut off from water, electricity and life-saving medical supplies, especially in rebel-held areas targeted by air strikes and ballistic missiles.
The Syrian government's restrictions on aid convoys have meant most supplies are distributed in government-held areas.
Peter Maurer, president of the International Committee of the Red Cross (ICRC), said aid workers had been able to do make more trips into opposition-held areas in the past two weeks, indicating Damascus may be softening its stance on convoys into such territory.
He said the workers were "not pleasantly surprised" by what they found in areas accessible for the first time, with the need for food, sanitation, water and medicine increasing.
"We saw devastation and destruction," he said. "What we were able to achieve is not enough. The needs are growing exponentially while our ability to react is growing linearly," he said.
Convoys and volunteers for the Syrian Arab Red Crescent -the ICRC's partner in Syria - have been targeted during the civil war by both sides, who are suspicious of the group's neutrality. Several volunteers have been jailed or killed.
Maurer called for aid groups to be respected. "When we have a convoy on the road from Damascus to any part of Syria it is of the uttermost importance that this convoy is allowed to pass checkpoints and is not shot at," he said at the end of a three-day visit to neighbouring Lebanon, which has 400,000 Syrian refugees.
The Syrian Observatory for Human Rights said on Monday that March was the bloodiest month yet in the conflict, with more than 6,000 people killed, a third of them civilians.
The group opposes Syrian President Bashar al-Assad but has monitored human rights violations on both sides.