The parade was in the south of the country. A separatist group, supported by the United Arab Emirates, held the parade for a group of new fighters on a football field. Many spectators were drawn to it.
Houthi rebels are probably behind the attack. The separatists and the Houthis have been fighting each other for years in southern Yemen. The southern separatists work together with the Saudi Arabian-led coalition that supports the internationally recognized Yemeni government.