There were conflicting reports on the place where the attack took place. While some reports said militants targeted a police headquarters in the Fua suburb, others suggested it happened at a military recruitment center. The local police chief survived the attack.
The terrorist detonated his suicide belt before the line of men at the security facility.
Sky News Arabia said that 30 people were killed and 70 wounded, Sputnik reported.
Al-Qaeda militants seized the port city of Mukalla last year, and it became a terrorist hotbed.
Since 2014, Yemen has been engulfed in a military conflict between forces loyal to fugitive former president president Abd Rabbuh Mansour Hadi and Houthi Ansarullah movement.
Since March 2015, the Saudi-led coalition of mostly Persian Gulf countries have been carrying out airstrikes against the Houthis at Hadi's request.