More than four million Syrians have fled into neighboring countries to escape the five-year-long civil war, the United Nations said Thursday.

In June, more than 24,000 people crossed into Turkey to escape fighting in northern Syria alone. The Syrian refugee population overall has grown by one million in just 10 months, the U.N. agency reported.

At least 7.6 million have been driven from their homes in Syria because of the fighting, international aid agencies say.

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"This is the biggest refugee population from a single conflict in a generation," Antonio Guterres, the United Nations high commissioner for refugees, said in a statement, noting that international aid is not on par with the scale of the crisis.

"Worsening conditions are driving growing numbers toward Europe and further afield," Guterres said, adding, "but the overwhelming majority remain in the region."

As many as 1.8 million Syrian refugees are taking shelter in Turkey, making it the biggest refugee population in the world. As many as 1.2 million Syrians are sheltering in Lebanon, more than 629,000 in Jordan and close to 250,000 in Iraq.

The U.N. appealed for $5.5 billion in aid in 2015 to deal with the Syria crisis, but by the end of June, the refugee agency said he had received less than a quarter of that amount.

"Part of the difficulty is that people have heard this before," Adrian Edwards, a spokesman for the agency, said. "I don't think there's an awareness of the degree of difficulty we are facing. It really is something of a crunch."

Meanwhile, more Syrian families will continue to suffer from poverty and hardship, the U.N. said.

(h/t The New York Times)