A Saudi Arabia-led military coalition was responsible for an "unacceptably high" 51 percent of child deaths and injuries in Yemen last year, according to a draft United Nations report seen by Reuters on Thursday.

The draft report on children and armed conflict, which still has to be approved by U.N. Secretary-General Antonio Guterres and is subject to change, blamed the Saudi-led coalition for more than 680 child casualties and three-quarters of the attacks on schools and hospitals in Yemen.

"Attacks carried out by air caused over half of all child casualties, with at least 349 killed and 333 injured," the draft report found. The Saudi-led coalition began an air campaign in Yemen in March 2015 to defeat Iran-allied Houthi rebels.