Turkey's foreign minister has said his country would keep its "open border policy" for refugees, but did not clarify when Syrians at the frontier could cross.
Speaking after a meeting with his EU counterparts in Amsterdam, Mevlut Cavusoglu said " we still keep this open border policy for these people fleeing from the aggression from the regime as well as air strikes of Russia".
Mr Cavusoglu indicated 50,000-55,000 refugees are making their way to the Turkish border from the nothern Syrian city of Aleppo, which aid workers say could soon fall under a government siege.
Earlier, Turkish Prime Minister Ahmet Davutoglu said 15,000 people fleeing Aleppo had arrived at Turkey's border, but some media reports put that number significantly higher.
Sitting in his car with his four children right inside the Turkish side of the border, 43-year-old Ahmet Sadul was hoping to get back into Syria so he could find his relatives.
A native of Syria's Azaz, he now lives in Kilis.
"Now there are thousands of people from Azaz all waiting on the other side. They escaped from Russians. I want to go and take my relatives. They are bombing Syrians all the time."
"Many people have left Aleppo. But still there are many civilians there. If Russia is successful, we are all dead."
Russia's intervention with air strikes to help longtime ally Syrian President Bashar al-Assad has tipped the war in Damascus' favour, reversing gains rebels made last year.
Turkey, which has taken in more than 2.5 million refugees fleeing the Syrian war, wants Mr Assad out and says only his removal can bring long-term peace.
Turkey has had an open-door policy to refugees since the start of the civil war, although some of the borders do get shut at times for security or other reasons.
Oncupinar has been officially shut since March due to security concerns, although authorities occasionally open it to take in refugees.
A 32-year-old customs police officer who works on the Syrian side of the border has said Russian warplanes have been bombing Syrian villages for 15 days.
"People are coming to the border and want to cross into Syria with the hope that they can sneak their relatives back into Turkey," he said.
"We are trying to save our relatives, our families."
Syrian regime warns against ground 'aggression'
The Syrian government has warned that its forces would resist any foreign ground intervention after reports Saudi Arabia and Turkey, which support rebel forces, could send in troops.
"Any ground intervention on Syrian territory without government authorisation would amount to an aggression that must be resisted," Foreign Minister Walid Muallem said at a news conference in Damascus.
"Let no one think they can attack Syria or violate its sovereignty because I assure you any aggressor will return to their country in a wooden coffin, whether they be Saudis or Turks," he warned.
