A Syrian refugee man walks between tents in Nizip refugee camp, near the Turkish-Syrian border in Gaziantep province, Turkey, Nov. 30, 2016. Photo: Reuters / Umit Bektas.

President Recep Tayyip Erdogan said on Thursday up to 250,000 migrants were fleeing toward Turkey from Syria’s northwest Idlib region after weeks of renewed bombardment by Russian and Syrian government forces.

Turkey already hosts some 3.7 million Syrian refugees, the largest refugee population in the world, and Erdogan said it was taking steps with some difficulty to prevent another wave from crossing its border.

With winter worsening an escalating crisis, the United Nations has said some 284,000 people had fled their homes as of Monday. Up to 3 million people live in Idlib, the last rebel-held swathe of territory after Syria’s nearly nine year civil war.

“Right now, 200,000 to 250,000 migrants are moving toward our borders,” Erdogan told a conference in Ankara. “We are trying to prevent them with some measures, but it’s not easy. It’s difficult, they are humans too.”

Towns and villages have been pounded by Russian jets and Syrian artillery since a renewed government assault last month, despite a deal agreed last September by the leaders of Turkey, Russia and Iran to ease tensions.

At least eight people, including five children, were killed on Wednesday in on Idlib town when the Syrian army launched missiles that struck a shelter for displaced families, witnesses and residents said.

In a report, the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said the city of Maarat al-Numan and the surrounding countryside “are reportedly almost empty.”

“Displacement during winter is further exacerbating the vulnerability of those affected. Many who fled are in urgent need of humanitarian support, particularly shelter, food, health, non-food and winterization assistance,” the OCHA said.

It said those displaced in December were fleeing toward Turkey, other parts of northern Idlib or toward other areas in northern Syria such as Afrin and al-Bab that Turkey seized in previous cross-border military operations.

Syrian President Bashar al-Assad, backed by Russia and Iran, has vowed to recapture Idlib. Turkey has for years backed Syrian rebels fighting to oust Assad.

Erdogan said last month his country could not handle a fresh wave of migrants from Syria, warning Europe that it will feel the impact of such an influx if the bombing is not stopped.

Moscow and Damascus both deny allegations of indiscriminate bombing of civilian areas and say they are fighting al Qaeda-inspired Islamist militants. However, their advances also pile pressure on Turkey, which has 12 military posts in the area.

On Tuesday, Turkish Defense Minister Hulusi Akar said it was out of the question for Turkey to evacuate its observation posts in Idlib.