The sources said it was not clear who was behind the attack which went off in a crowded market where the drug qat is sold.
Renewed fighting across Yemen is threatening to wreck a truce that had largely held since April 10, buttressing a round of UN-backed peace talks in Kuwait aimed at ending the country's civil war.
Saudi Arabia and its Gulf Arab allies intervened in Yemen's civil war on March 26 last year in support of the government after it had been forced into exile by the Iran-allied Houthi group.
The war has killed more than 6,200 people, displaced more than 2.5mn and caused a humanitarian catastrophe in one of the world's poorest countries.
