(CNN) The Saudi-led coalition fighting Houthi rebels in Yemen acknowledges "mistakes" were made in last month's deadly airstrike on a school bus in northern Yemen, the Saudi Press Agency said Saturday.

The attack killed 51 people, including 40 children , according to the Houthi-held Health Ministry. The coalition cited "mistakes in compliance to the rules of engagement."

The children had been on a field trip to a graveyard for rebels, one of the few green spaces left in Yemen's Saada governorate.

In a statement, the command issued "regret over the mistakes, extends its sympathies and solidarity to the families of the victims." It issued its conclusions after reviewing the findings of an assessment team.

"The Joint Forces Command will, as soon as the official findings are received, undertake legal proceedings to hold the ones who committed mistakes accountable according to the rules and regulations related to such cases," the coalition said.