File picture: Xinhua/Faisal Isse

Mogadishu, Somalia - An Islamic extremist suicide bomber disguised as a police officer killed at least 17 and injured 20 at a police academy in Somalia's capital on Thursday, police said.

Col. Mohamud Aden said that 20 other officers were wounded by the blast, some of them seriously.

The bomber, with explosives strapped around his waist and torso, infiltrated Gen. Kahiye Police Academy and targeted officers gathering for special morning exercises, Capt. Mohamed Hussein said. The officers were rehearsing for Somalia's Police Day celebrations scheduled for Dec. 20, Hussein said.

The bomber walked into the police academy undetected and joined a long line of officers in the rehearsal parade before he detonated the explosives under his sportswear, Hussein said.

"He detonated his bomb vest having realized that his presence had drawn suspicion among officers in the queue," he said.

Police officer Farah Omar who was at the scene at the time of the blast said the bomber targeted a spot where dozens of soldiers had gathered.

"He wanted to inflict a maximum damage," said Omar.

The Somalia-based al-Shabab extremist group quickly claimed responsibility for the attack. Al-Shabab, which is allied to al-Qaida, carries out frequent bombings and attacks against hotels, checkpoints and other high-profile areas of Mogadishu.

Al-Shabab has been blamed for the massive truck bombing in the capital in October that left 512 dead. Only a few attacks since 9/11 have killed more people.

Al-Shabab has become the deadliest Islamic extremist group in Africa and is increasingly targeted by the U.S. military after the Trump administration early this year approved expanded airstrikes and other efforts against the fighters.

The U.S. has carried out at least 32 drone strikes this year against al-Shabab and a small but growing number of fighters linked to the Islamic State group, many of them defectors from al-Shabab.

A drone strike earlier this week against an al-Shabab vehicle carrying explosives prevented an "imminent threat to the people of Mogadishu," the U.S. Africa Command said.

Associated Press