UNITED NATIONS (AP) — The U.N. humanitarian chief warned Wednesday that the growing number of Syrians fleeing the country's increasingly brutal conflict — now 4 million and rising every day — is outstripping the international community's ability to help.

Valerie Amos told reporters after briefing the Security Council that "this is a crisis that is completely stretching our capacity."

She said she is extremely concerned about the rising cost, noting that the U.N. has received only $200 million of the more than $1.5 billion pledged for Syria at a Jan. 30 donor's conference in Kuwait. The $1.5 billion was supposed to cover humanitarian needs in Syria for six months but that projection, from the end of the year, is already out of date, she added.

"I think the first two months of this year have been a real game-changer," Amos said. "It demands more of us in terms of our ability to scale-up our operations, but ... even with us working full-tilt, the scale is out-pacing whatever we do on the response side."

On a positive note, she said, her office has been able recently to cross "conflict lines" between opposition and government-controlled areas to help people in need in the cities of Homs and Idlib. But the Syrian government is still refusing to allow aid to enter from Turkey, leaving thousands of people trapped without aid, she said.

Amos said she and U.N. refugee chief António Guterres delivered the same warning to the Security Council during the closed-door briefing.

Guterres, speaking by videoconference to the council, warned that a "moment of truth" was approaching in Syria and that the international community must not allow the situation to deteriorate further, according to quotes released by his office.

"What is happening in Syria today risks escalating very quickly into a disaster that could overwhelm the international response capacity — political, security-related and humanitarian," he warned. "This must not be allowed to happen."

Guterres called the humanitarian situation "dramatic beyond description" and said "the refugee crisis is accelerating at a staggering pace, month after month."

He noted that in April 2012, about a year after the conflict began, there were 33,000 registered refugees in the region. Continued...