France and Britain called Thursday for an emergency U.N. Security Council meeting to press Syria's warring parties to lift sieges on towns where hundreds of thousands have been cut off from aid and reports of starvation have emerged.

U.N. Secretary-General Ban Ki-moon also stepped up the pressure, calling for both the Syrian government and rebels to end the sieges before peace talks scheduled for Jan. 25 in Geneva as a confidence-building measure.

Ban said the United Nations and its humanitarian partners are able to deliver food to only 1 percent of the 400,000 people under siege in Syria, down from an already dismal 5 percent just over a year ago.

"This is utterly unconscionable," Ban said at a news conference.

Ban said both the Syrian government and rebels are committing war crimes by deliberately starving civilians and must face justice.

"U.N. teams have witnessed scenes that haunt the soul. The elderly and children, men and women, who were little more than skin and bones: gaunt, severely malnourished, so weak they could barely walk, and utterly desperate for the slightest morsel," Ban said. "I would say that they are being held hostage — but it is even worse. Hostages get fed."

France's U.N. mission said a request for an emergency meeting was made Thursday to Uruguay, which holds the rotating Security Council presidency. Britain's mission said the meeting was requested for Friday afternoon, but it has not yet been scheduled. The United States was initially reported as a sponsor of the meeting but its mission said it had not called for it.

Trucks from the U.N. and other humanitarian organizations entered three besieged communities in Syria this week for the first time in months.

The town of Madaya has been under siege for months by forces loyal to Syrian President Bashar Assad. The two other towns, Foua and Kfarya, have been besieged by Syrian rebels.

Earlier this week, Syria's U.N. ambassador, Bashar Ja'afari, dismissed the reports of starvation in Madaya as lies.

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Associated Press writer Edith M. Lederer contributed to this story from the United Nations.