The number of Syrians refugees who have fled their country in two years of conflict reached the one million mark, the U.N. refugee agency (UNHCR) announced Wednesday.

Syrians seeking refuge in neighboring countries have jumped dramatically since the beginning of the year, with more than 400,000 people leaving since Jan. 1.

About half of the refugees are children, the majority under the age of 11, the U.N. said. The largest number of refugees has fled to Lebanon, Jordan, Turkey, Iraq and Egypt. Increasingly, Syrians are also fleeing to North Africa and Europe, according to the U.N. data.

U.N. High Commissioner for Refugees António Guterres said refugees' arriving in neighboring countries has had a “severe” impact on the host countries.

Lebanon's population has increased by as much as 10 percent, while Jordan's energy, water, health and education services are being strained to the limit, the UNHCR said in a statement. Turkey has spent over $600 million setting up 17 refugee camps, with more under construction. Iraq, juggling its own crisis with more than one million Iraqis internally displaced, has been home to more than 100,000 Syrian refugees in the past year.

"With a million people in flight, millions more displaced internally, and thousands of people continuing to cross the border every day, Syria is spiraling towards full-scale disaster,” Guterres said in the statement. "We are doing everything we can to help, but the international humanitarian response capacity is dangerously stretched. This tragedy has to be stopped."

He added that the countries hosting the refugees “should not only be recognized for their unstinting commitment to keeping their borders open for Syrian refugees, they should be massively supported as well.”

“We are constantly shocked by the horrific stories Syrian refugees tell us. Their lives are in turmoil. They have lost their homes and family members. By the time they reach the borders, they are exhausted, traumatized and with little or no resources to rely on,” Panos Moumtzis, UNHCR Humanitarian Coordinator for the Syria Emergency said in a statement appealing for donations.

The British government’s International Development Secretary Justine Greening Wednesday urged international donors to deliver the humanitarian help they had promised earlier.

In a massive funding drive in Kuwait in January, international donors had committed over $1.5 billion for the humanitarian crisis in Syria. The bulk of the cash was pledged by Gulf countries with Kuwait, Saudi Arabia and Qatar promising $300 million each. But the U.N. said funding was not being delivered quick enough.

“One million refugees is a terrible landmark and the most vulnerable groups are inevitably those who find themselves at greatest risk. Syria’s neighbors cannot deal with this alone and all donors must rapidly deliver on the promises they made in Kuwait,” Greening said in a statement released by her department.

The statement noted that at least four million more people are in desperate need of humanitarian assistance inside Syria.

“We are working closely with agencies on the ground. Britain has never stood on the sidelines and we are determined to make sure our support gets help to those in need as quickly and effectively as possible,” she said.

On Tuesday, Jordan's King Abdullah called on world nations to help his country, Turkey and Lebanon to bear “the tremendous burden” of caring for the huge influx of people, the BBC reported.

A UN report released Tuesday said that thousands of schools have been damaged or converted into shelters for civilians displaced by civil war and that attendance rates of teachers as well as students have plummeted since the start of the civil war.

The assessment by UNICEF, or the United Nations Children’s Fund, said one-fifth of the country’s schools have suffered direct physical damage or are being used to shelter internally displaced persons (IDPs) with cities of Idlib, Aleppo and Deraa being the worst hit.

UNICEF found, based on data collected in December, that more than 110 teachers and other staff have been killed and many others are no longer reporting for work.

“The education system in Syria is reeling from the impact of violence,” UNICEF’s Syria Representative, Youssouf Abdel-Jelil said in a statement published on its website. “Syria once prided itself on the quality of its schools. Now it’s seeing the gains it made over the years rapidly reversed.”

The U.N. agency is currently supporting more than 170 school clubs, which allow some 40,000 children to receive remedial education and take part in recreational activities, in Homs, Deraa, rural Damascus, Tartous, Lattakia, Hama, and Quneitra.

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