Aden is the temporary base of Yemen's internationally recognised government, which has been battling Iran-backed rebels as well as jihadists across the country for more than a year.
Security officials told AFP that the attacker drove an explosives-laden vehicle into a gathering of army recruits at a school in northern Aden early Monday.
Although the school was locked as recruits registered inside, the attacker drove in when the gate was opened for a delivery vehicle, officials said.
The assault killed at least 60 people and wounded 29 others, medical sources from the three hospitals where the victims were taken told AFP.
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They could not immediately verify if all those killed were recruits.
Aden has seen a wave of bombings and shootings targeting officials and security forces.
Attacks in the port city are often claimed by jihadists from either Al-Qaeda or IS, who have both taken advantage of the chaos in Yemen to make gains in southern and southeastern regions.
Yemeni authorities have trained hundreds of soldiers in Aden over the past two months as part of operations to retake neighbouring southern provinces from jihadists.
Earlier this month, Yemeni government forces backed by a Saudi-led coalition entered Abyan's provincial capital Zinjibar.
Troops retook other towns across Abyan but have been met by fierce resistance in the key Al-Qaeda stronghold of Al-Mahfid, security sources said.
The militants are still present in areas surrounding the recaptured towns and control large parts of the neighbouring Shabwa province, the sources say.
The coalition intervened in Yemen in March last year and helped government troops push the rebels out of Aden and four other southern provinces.
More than 6,600 people, mostly civilians, have been killed in Yemen since March 2015 and more than 80 percent of the population has been left in need of humanitarian aid, according to the UN.
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