A car bomb exploded at a hospital used as a base by Yemen's Shi'ite Muslim Houthi movement on Sunday, killing or wounding dozens of people, tribal and local sources said.
The attack took place in Marib province, east of the capital Sanaa, the sources said.
Houthi fighters seized Sanaa on Sept. 21 after four days of fighting with soldiers loyal to the Sunni Muslim Islah party. They have since refused to quit the capital, despite an agreement they signed with President Abd-Rabbu Mansour Hadi to make them a part of the government.
The stability of Yemen is a priority for the United States and its Gulf Arab allies because of its position next to Saudi Arabia and shipping lanes which run through the Gulf of Aden.
Saudi Foreign Minister Prince Saud al-Faisal told the U.N. General Assembly on Sunday that the situation in Yemen posed a threat to international security, and said the agreement to form a new government had been wrecked by the Houthis' failure to give up control of the capital.