BUDAPEST/ONCUPINAR, Turkey (Reuters) - Turkey is admitting Syrian refugees in a “controlled manner” and has let in thousands fleeing Russian air strikes, its foreign minister said on Tuesday, warning the numbers of new migrants could reach a million if the attacks continue.

Syrians line up as they wait to cross into Syria at Oncupinar border crossing in the southeastern city of Kilis, Turkey February 8, 2016. REUTERS/Osman Orsal

An assault by Russian-backed Syrian government forces around the city of Aleppo has sent more than 30,000 people fleeing to the Turkish border gate of Oncupinar in the past few days, and officials say tens of thousands more could be on the move.

Foreign Minister Mevlut Cavusoglu said Turkey had so far let in 10,000 people from the latest wave, but it was not immediately clear where on the border he was referring to.

Oncupinar has remained closed in recent days to all but the most seriously wounded, some of them crossing by foot or brought in by ambulance, according to Reuters witnesses.

The United Nations and European Union have urged it to open the crossing.

“Recently more than 50,000 people came to the border with Turkey due to Russia’s air attacks. We took in 10,000 of these migrants and we are building some camps at the other side of the border for some,” Cavusoglu said during a visit to Budapest.

“We are allowing in those who want to come, in a controlled fashion,” he told a news conference with his Hungarian counterpart.

“MORAL AND LEGAL DUTY”

The bulk of the refugees at Oncupinar are being cared for at Bab al Salama, on the Syrian side of the border, with Turkish aid groups trucking across food and supplies.

The United Nations on Tuesday urged to Turkey open the border and called on other countries to assist it with aid. The European Union, which has agreed a 3 billion euro fund to improve conditions for refugees in Turkey, has said Ankara has a moral and legal duty to care for them.

Turkey has won international praise for its hosting of more than 2.5 million refugees, but amid pressure from the EU to prevent them traveling on to Europe there are signs that its open door policy may be starting to tighten.

Most border crossings are now closed, although it has opened some of them on occasion for humanitarian emergencies.

Several thousand Turkmen and Arabs fleeing advancing pro-government Syrian forces in the north of Latakia province further west were let into Turkey a week ago, some evacuated for security reasons from a camp on the Syrian side.

Turkish aid officials said around 5,600 people had been let in near the border town of Yayladagi between Jan. 28 and Feb. 2.

Cavusoglu said the latest influx could reach hundreds of thousands or even a million if the offensive by Syrian government forces in the countryside around Aleppo, once Syria’s biggest city with 2 million people before the war, continued.

The fighting is approaching the Turkish border and President Tayyip Erdogan has said the refugees at Oncupinar will be allowed in if necessary.