Tens of thousands of people are fleeing Syria as the Islamic State (IS) militant group expands its grip on large parts of the country despite a US-led air campaign, the United Nations has said.
UN humanitarian chief Valerie Amos said tens of thousands more civilians could flee if fighters with Islamic State - also known as Isil or Isis - continue to seize control of territory.
"Over the past two weeks, Isil forces have advanced in northern Aleppo and over 160,000 people, mostly women and children, fled into Turkey in just a few days," Baroness Amos told the Security Council.
"Their fear is so great that many people crossed heavily mined fields to seek refuge."
More than a week has passed since the US and Arab allies began air strikes against IS camps and other assets inside Syria. It has created an unusual situation where the US, which opposes Syrian president Bashar Assad, and Syria's government are on the same side against the extremist group.
Syria has said the US informed it of the first air strikes but has given no further notifications as the campaign continues.
The rise of IS has complicated Syria's brutal civil war, now in its fourth year, which has already forced three million registered refugees into neighbouring countries. Baroness Amos told the Security Council that the actual number is "far higher than that".
"Those who can, flee," she said simply.
Her monthly briefing on Syria's humanitarian situation remained bleak, despite the opening of the Qamishli border crossing with Turkey that Baroness Amos said will help get aid to another 225,000 people.
In July, the Security Council unanimously approved the delivery through four border crossings with Turkey, Jordan and Iraq without the approval of the Syrian government, which Baroness Amos has blamed repeatedly for slowing the aid process.
The UN has blamed the Syrian government and armed rebels for what Baroness Amos called "utter disregard for international humanitarian and human rights law", with violence on both sides causing civilian deaths.
She said 11 million people inside Syria still need urgent aid. She welcomed the billion dollars pledged last week by various parties during the UN General Assembly but said more is needed. "Without additional funds, the World Food Programme will be forced to end its operations completely within two months," she said.