Islamic State claimed responsibility for the attack, the latest in a series of bombings rattling the city since Saudi-backed forces captured Yemen’s second-largest city from the Iran-allied Houthis in July last year.
At least 60 people were also wounded in the attack targeting hundreds of new recruits at the Ras Abbas camp in Aden’s Buraiqa district. It was recently set up by Hadi’s government to absorb new conscripts being trained to fight the Houthis.
The official said the bomber was disguised in military uniform used by the new recruits, enabling him to penetrate the crowd undetected inside the camp.
An official earlier said the attack occurred at the gate.
Witnesses described ambulances racing to evacuate the wounded, as troops surrounded the area to keep onlookers away.
“The explosion shook the camp violently and it could be heard miles away,” one witness told Reuters by telephone.
Medics at the nearby Masafi hospital said they had received the bodies of 13 people, while at least 60 wounded people were taken to hospitals in Aden.
Islamic State, in a statement published on its online media arm Amaq, said that a bomber wearing an explosives vest blew himself up at the Ras Abbas camp. The group published a photo of the attacker it identified as Abu Isa al-Ansari, and said the bombing “killed around 20 apostates and wounded 60 others”.
Residents had said that Islamic State, one of several armed groups that operate in southern Yemen, had recently warned young Yemenis against joining the army being set up by Hadi’s government.
On Tuesday, Aden’s governor and security director survived a gun attack by unknown assailants on their convoy in the city.
Last month, a suicide bomber killed six people in an attack on a checkpoint on the road leading to Hadi’s presidential palace in Aden.