On Sunday, Saudi Arabia's foreign minister refused calls from Tehran to stop its aerial assault. Iran supports the Houthis, who are fellow Shiites, but both Tehran and the rebels deny it arms them.

Prince Saud al-Faisal said his country is not at war with Iran, but charged Tehran with fueling the cycle of violence in Yemen. Riyadh and Tehran are longtime regional rivals, and also back opposite sides in Syria's civil war.

"Iran is not in charge of Yemen," al-Faisal said during a press conference Sunday in Riyadh alongside his French counterpart, Foreign Minister Laurent Fabius.

Saudi military spokesman Ahmed Asiri said during a briefing Sunday that airstrikes hit an airport in the Houthi stronghold of Saada, as well as areas used by the Houthis and their allies in Shabwa, Sanaa, Taiz and Aden.

He added that the Saudi government is coordinating with some of the tribes in Yemen.

Sunday's airstrikes in the oil- and gas-rich north-central province of Marib hit groups of Houthi and allied fighters, Yemeni security officials said. All officials spoke on condition of anonymity because they were not authorized to speak to journalists.

Sheikh Saleh al-Anjaf, spokesman for an alliance of Marib-based tribes, said Houthis and Saleh loyalists tried to advance from the ancient ruins of Sirwah but were pushed back following a fierce battle with tribesmen.

Al-Anjaf said six tribesmen were killed and seven wounded in the fighting and that the tribe took six Houthi fighters hostage. The Houthis did not announce any casualties, and Houthi officials could not be reached for comment.