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Aid workers must be given access if parts of Syria come under a cease-fire to allow chemical weapons experts to try to bring the country's stockpile under international control, the head of the U.N.'s World Food Program said.

Ertharin Cousin told The Associated Press in an interview Monday that an agreement under discussion now envisions a cessation of hostilities so chemical experts can travel across the country, including to many conflict areas where WFP and other humanitarian workers have been unable to bring in desperately needed aid.

"So this is an opportunity for us to hopefully overcome the hurdle that today we've been unable to achieve," she said.

The United States and Russia brokered an agreement for Syria to give up its chemical weapons but U.N. diplomats say they are at odds on details of a U.N. Security Council resolution spelling out how it should be done and the possible consequences if Syria doesn't comply.

Cousin urged the international community to demand that the Security Council make any cease-fire a broad one.

"When you talk about a cessation of hostilities to allow access for the chemical (weapons) workers, that cessation in hostilities should also allow access for humanitarian workers," she said.

WFP is currently feeding 3 million people inside Syria and 1.2 million in neighboring countries. Cousin said the goal is to step up supplies so that 4 million internally displaced people and 1.5 million refugees are getting food by the end of October.

While the agency is working in all 14 Syrian governorates, Cousin said there are pockets in many of them that humanitarian workers can't reach because of fighting.

The opposition Syrian National Coalition accused government forces Monday of tightening their siege during the past month in the Damascus suburb of Ghouta, where U.N. inspectors reported that chemical weapons were used in an Aug. 21 attack.

"Assad's forces are starving people to death in those areas," the coalition claimed. "The specter of famine looms in the horizon as more than 2 million people remain under siege."

Cousin said WFP hasn't had access to an opposition-controlled area in Ghouta called Muhammadiyah, which is besieged by government forces. She also pointed to an area in the Kurdish-dominated Hasaka region in the northeast controlled by the al-Qaida-linked Nusra Front and an opposition-controlled area on the outskirts of the northern city of Aleppo where the agency has had trouble operating.

Cousin said the bullets that have been fired at WFP trucks trying to get into Ghouta and other conflict areas "don't say 'I came from the regime' or 'I came from the opposition.'"

"The reality of it is there's enough complicity to go around," she said.

WFP has tried to identify third party monitors who can access these difficult areas, Cousin said.

"The challenge is the same — getting third party monitors and food into these areas," she said. "So it's an awful Catch-22. You need to get the monitors in so you can justify the access that is necessary to get food in."

As Syrians prepare to face their third winter in conflict, thousands including women, children and seniors, need food, medicine, blankets and other humanitarian aid, she said.

"So we must demand that all the parties ... provide access to humanitarians," Cousin stressed, adding that she has been talking to prime ministers, foreign ministers and anyone else with influence on the five permanent Security Council members who hold the key to the contents of the chemical weapons resolution.

She said WFP's traditional donors — the U.S., U.K., European Union, Germany and Canada — have been generous with money to support the massive feeding program in Syria, which is costing $30 million a week. But more help is needed.

"We need the entire global community, which means we need Saudi Arabia, we need China" and others, Cousin said.

She said donor fatigue is a concern.

"What worries me more than the fact that there's not a bottomless pit is the escalating cost and ... the impact that that will have on other crises around the world," Cousin said. "The problems in Somalia, the Sahel, Yemen, didn't disappear because the problems in Syria are increasing. What we can't afford is to prioritize one hungry child over another."