Police investigators said the attack bore the hallmarks of al Qaeda.

Medics said dozens of people were also injured in the attack, which appeared to have been timed to coincide with the cadets leaving the academy at the end of the school day.

Witnesses said police closed the scene of the attack and began investigating the blast as ambulances ferried casualties to hospital.

The attack appeared to mirror a suicide bombing in May, when a suicide bomber in army uniform struck at the heart of Yemen’s military establishment, killing more than 90 people during a rehearsal for an army parade in Sanaa.

That attack was claimed by al Qaeda in the Arabian Peninsula (AQAP), which US officials have described as the most dangerous grouping of the global militant network.

Islamist militants linked to al Qaeda have vowed to carry their fight across Yemen after a US-backed military offensive in May drove them out of strongholds they took last year during protests against former President Ali Abdullah Saleh’s rule.

A number of attacks since the recent offensive indicate that the militants still pose a serious threat.