Yemeni security officials say Houthi rebels are blocking humanitarian aid to the besieged western city of Taiz.
The officials say 18 trucks from the World Food Program were prevented from leaving the city of Ibb, north of Taiz, on Sunday. Taiz has been besieged by Houthi rebels and allied forces for the past year.
The attempt to deliver aid to Taiz came during a 48-hour truce announced on Saturday by the Saudi-led coalition, which is backing the internationally-recognized government against the Houthis.
The WFP did not immediately respond to a request for comment.
The officials spoke on condition of anonymity because they were not authorized to speak to the press.