The civilians were killed and 10 others wounded in Sa'ada province after attacks on a house and a private vehicle, the UN's Humanitarian Coordinator in Yemen Jamie McGoldrick said, citing reports from fellow aid groups.
Reuters reported on Friday that three women and six children from the same family were killed in an airstrike by the Saudi-led coalition on their home in the area, according to a local health official.
A spokesman for the Saudi-led coalition did not respond to a request for a comment.
The new incidents were an example of the "brutality" of the conflict, McGoldrick said in the statement in which he expressed deep concern.
"All parties to the conflict continue to show a disregard for the protection of civilians and the principle of distinction between civilians and combatants in the conduct of hostilities."
Sa'ada, a stronghold of the Houthi movement, has been repeatedly hit by airstrikes since the coalition of Arab states joined the civil war in March 2015.