The United Nations says donors have pledged $250 million to educate over one million Syrian refugee children this year but it urgently needs an additional $500 million to fund the program in Turkey, Lebanon and Jordan.

The U.N. envoy for global education, Gordon Brown, made the announcement Tuesday and pledged to try to raise the rest of the money in the next month.

Brown, the former British prime minister, said in a statement that "death voyages to Europe" will soar in 2016 as long as Syria's six million displaced children and two million refugee children "are exploited and denied any opportunity within the region."

He said child marriage rates for Syrian refugee girls have doubled, and a recent survey estimates that one in three boys and girls have become child laborers.