CAIRO (AP) — A humanitarian group says that attacks on Yemeni civilians are "unacceptable" but have taken on a chillingly regular frequency, a day after an airstrike by the Saudi-led coalition targeting Yemen's Shiite rebels killed some 17 people in the port city of Hodeida.

In a statement Sunday, the Norwegian Refugee Council said "attacks that kill and maim civilians are no longer an anomaly in Yemen's war."

On Saturday, Yemeni rebel officials said that the airstrike in the Jebel Ras area also wounded 20 people when it hit near a minibus.

Hodeida, with its key port installations that bring in U.N. and other humanitarian aid, has become the center of Yemen's conflict, with ground troops allied to the coalition struggling to drive out the rebels controlling it.