Yemeni officials say a helicopter gunship belonging to the Saudi-led coalition targeting Yemen's Shiite rebels has hit a truck in the country's north, killing nine people travelling in the vehicle.

Security and military officials say the attack took place early on Thursday in the northern Saada province, which is a stronghold of the Iran-backed rebels known as Houthis.

The officials say the truck was suspected of carrying rebel weapons. They spoke on condition of anonymity because they are not authorized to speak to the media.

The Houthis last year captured Yemen's capital, Sanaa, and much of the country's north.

The attack came on the second of a five-day humanitarian cease-fire that began nearly seven weeks after the coalition began airstrikes against the Houthis and their allies.