Kurdish security control the flow of Syrian refugees trying to cross into northern Iraq from northeastern Syria on Oct. 23, 2013. Mauricio Morales/AFP/Getty Images

The U.N. estimates that about 9.3 million people in Syria, or about 40 percent of the population, need humanitarian assistance owing to the country's ongoing civil conflict.

Valerie Amos, the U.N. humanitarian chief, told the 15-member Security Council on Monday that 9.3 million people now need outside help to survive, up from 6.8 million in September. She said 6.5 million are now homeless inside the country, up from 4.25 million.

The population of Syria is about 23 million.

"The humanitarian situation inside Syria continues to deteriorate rapidly and inexorably," she said during a closed-doors meeting, according to her spokeswoman Amanda Pitt.

Pritt said Amos continued to press the council to influence parties "who can ensure the protection of civilians and civilian facilities" and the safe passage of medical personnel, supplies and humanitarian assistance, "and can facilitate progress in expanding critical, life-saving relief operations."

Amos' plea to the Security Council follows the Syrian government's promise Monday to ensure delivery of vaccinations and humanitarian aid across the country after an outbreak of polio in the northeast and warnings of malnutrition in areas under military siege.

Twenty-two children in Deir Ez-zor province bordering Iraq were left paralyzed last month.

Ten of the children are confirmed to have the polio virus so far, and experts say it could spread quickly across the region.

Last month Amos demanded stronger action by the Security Council to get aid into Syria, where millions of people in need have not received any help for almost a year.

Violence and excessive red tape have slowed aid delivery to a trickle in Syria. More than 100,000 people have been killed in the civil war and millions have fled the country.

After months of talks, the Security Council approved a non-binding statement on Oct. 2 urging increased humanitarian access.

Amos has complained that the statement has had little impact on the ground.

Senior U.N. diplomats say that Russian foreign minister Sergey Lavrov has dismissed the possibility of a legally binding resolution on aid access in Syria.