A U.N. humanitarian agency says thousands of Yemeni civilians caught in fierce clashes between warring factions are trapped in an embattled northern district.

The U.N. Office for the Coordination of Humanitarian Affairs, or OCHA, says the number of displaced in the district of Hajjah has doubled over the past six months.

Tuesday's report by OCHA says the impoverished governorate is home of Yemen's most recent flashpoint district of Kusher where "thousands of civilians are reportedly trapped between conflicting parties."

Over the past two days, airstrikes by the Saudi-led coalition, which is fighting on behalf of Yemen's internationally recognized government, have killed 22 people, including women and 14 children in the area.

Yemen's Houthi rebels are trying to gain control of Kusher after local tribesmen took up arms against the Houthis.