The United Nations said Friday that a Saudi-led airstrike had killed at least 22 children and four women in Yemen as they fled a fighting zone — the second mass killing of Yemeni civilians by Saudi Arabia and its military partners in two weeks.

Mark Lowcock, the top United Nations relief official, asserted without qualification that the Saudi-led coalition warring with Yemen’s Houthi rebels was responsible for the attack, which happened on Thursday in a pro-Houthi district near the Red Sea port of Al Hudaydah. He said an additional airstrike in the area had killed four more children.

The assertion by Mr. Lowcock, in a statement on his office’s website, came as the Saudi coalition and the Houthis were accusing each other of the attack, which has underlined the vulnerability of civilians in a war that has lasted more than three years and become what the United Nations considers the world’s worst man-made humanitarian crisis.

Criticism of Saudi Arabia and its partners has been growing over thousands of civilian casualties, many of them caused by munitions fired from the coalition’s warplanes.