About 60,000 Syrian Kurds fled into Turkey in the space of 24 hours, as so-called Islamic State militants seized dozens of villages close to the border.
Turkey opened a stretch of the frontier yesterday after Kurdish civilians fled their homes. They are fearing an imminent attack on the border town of Ayn al-Arab, also known as Kobani.
A Kurdish commander on the ground said the so-called Islamic State had advanced to within 15km of the town.
Local Kurds said they feared a massacre in Kobani, whose strategic location has been blocking the radical Sunni Muslim militants from consolidating their gains across northern Syria.
The US has said it is prepared to carry out airstrikes in Syria to stop the advances of the so-called Islamic State.
It has also seized tracts of territory in neighbouring Iraq and has proclaimed a caliphate in the heart of the Middle East.
US forces have bombed the group in Iraq at the request of the government.
It is unclear when or where any military action might take place in Syria, whose president, Basha ral-Assad, Washington says is no longer legitimate.