The number of Syrians trying to cross into Turkey amid an upsurge of fighting in northern Syria has nearly doubled, a Turkish official says.
The governor of the Turkish border province of Kilis said 35,000 refugees had reached the border area - up from an estimated 20,000 on Friday.
Turkey says it is prepared to help the refugees but the frontier remains shut.
They are fleeing a Syrian government offensive on rebel-held positions near the northern city of Aleppo.
In the past few days, the Syrian army - backed by Russian air strikes - has made a series of gains around Syria's largest city.
In other developments:
About 120 fighters on both sides were killed around the town of Ratyan, north of Aleppo, on Friday, the UK-based Syrian Observatory for Human Rights says
Syrian FM Walid al-Moualem warns the country will resist any intervention and the aggressors would be sent home "in coffins", in a what is seen as a reference to Saudi Arabia's statement that it may join such an operation
Nato accuses Russia of "undermining" Syrian peace efforts - including the suspended talks in Geneva - through its strikes, a claim denied by Moscow
Russia and Turkey trade accusations of preparing an invasion in Syria
Turkey's 'obligation'
On Saturday, Kilis Governor Suleyman Tapsiz said Turkey was able to help refugees inside Syria.
"Our doors are not closed, but at the moment there is no need to host such people inside our borders," he said.
Turkey has been providing food, shelter and blankets to thousands of civilians who are stranded on the Syrian side of the border.
Who is to blame for peace talks' suspension?
Displaced Syrians struggle to survive
The story of the conflict
map
The Turks have so far refused to open the border crossing.
EU Enlargement Commissioner Johannes Hahn on Saturday urged Turkey to do so.
"The Geneva convention is still valid which states that you have to take in refugees," Mr Hahn said, as EU foreign ministers discussed the crisis in Amsterdam.
The call was echoed by Dutch Foreign Minister Bert Koenders, whose country currently holds the EU presidency.
"I look at these images of people standing at the Turkish border and I just wanted to underline the message people who are in humanitarian need should be allowed in," he said.
Syrians queue for aid at the Bab al-Salam border gate, on the Syrian border with Turkey, 5 FebruaryImage copyrightAP
Waiting at the gates: Mark Lowen, BBC News, reports from Gaziantep
The thousands fleeing Aleppo have spent their first night in temporary shelter at the Turkish border but the crossing remains closed.
Turkey has welcomed more than two million Syrians since the start of the war and it is unclear whether it will accept another huge wave in one go.
Human rights groups are calling for the gates to open but at a time when the EU is trying to reduce the flow of refugees to Europe, there will be diplomatic pressure on Turkey to act with caution.
The Turkish government is using the new refugee exodus to take aim at Russia, whose air strikes on Aleppo have prompted thousands to flee. But there is no sign that Russia is pulling back and as opposition fighters retreat, the Assad regime is strengthened and thousands more civilians will flee, hoping for sanctuary in Turkey.
In November, the EU clinched a deal with Turkey, offering it €3bn (£2.3bn; $3.3bn) to care for Syrian refugees on Turkish soil.
On Thursday, 60 donor countries meeting in London pledged billions of dollars to ease the plight of Syrian refugees.
About 4.6 million people have fled Syria during the civil war that began in 2011. Another 13.5 million are said to be in need of humanitarian assistance inside the country.
Turkey hosts the largest number of refugees - 2.5 million.
The Syrian war and Aleppo
A map showing how Syrian government forces have gradually surrounded Aleppo
March 2011: Anti-government protests erupt across Syria, but Aleppo is initially untouched as a result of a state crackdown
February 2012: As the rebellion turns into a conflict, clashes between rebels and the government are reported with increasing frequency in Aleppo province
July 2012: The battle for Aleppo begins. Rebels make swift advances, but are unable to consolidate their gains and the city becomes divided
2013: The government begins bombarding rebel districts with barrel bombs, causing thousands of casualties
September 2015: Syria launches a fresh offensive in the wake of Russia's intervention in the conflict
February 2016: The government captures towns north of Aleppo, threatening to encircle the city