World Bulletin / News Desk
A bomber rammed his explosives-laden vehicle into a building of pro-government forces in northern Aden as they were having their breakfast.
Another source said 15 fighters were killed and scores injured. Both sources spoke on condition of anonymity due to security concerns.
A source with Doctors Without Borders (MSF) medical charity group said 25 bodies have been transferred to hospitals.
The source expected the death toll to rise as many of the injured are in a critical condition.
There has been no claim of responsibility for the attack.
Yemen has been ravaged by civil war since late 2014, when Houthi rebels overran capital Sanaa and a number of other provinces, forcing the government of President Abd Rabbuh Mansour Hadi to flee to Saudi Arabia.