Medical officials have raised the toll from Saudi-led airstrikes on a convoy of civilians fleeing the fighting in southern Yemen to 31, making it among the deadliest single attacks since the air campaign began nearly three months ago.

The officials say the attack took place early Wednesday in the northern outskirts of the southern port city of Aden, which has seen months of intense fighting between Shiite Houthi rebels and their opponents.

The officials say those killed were families carrying food and personal belongings, fleeing north in a convoy of vehicles, including a bus carrying 16 passengers. The officials insisted on anonymity because they were not authorized to speak to the media.

The Saudi-led coalition launched an air campaign against the Iran-backed Houthis in late March.