A suicide bomber driving a minibus killed at least 30 people Wednesday as cadets gathered to enroll at a police academy in the heart of Yemen’s capital, Sanaa, authorities said.

The blast wounded dozens of people, officials initially said. The officials spoke on condition of anonymity as they weren’t authorized to brief journalists.

At the scene of the blast, the dead and wounded lay on a sidewalk against a wall. Water sprayed by firefighters to extinguish the blaze mixed with their pooled blood. A charred taxi cab smoked near what remained of the minibus, meters (yards) from a gate for the police academy.

The bomber struck as lines of cadets waited outside of the academy, preparing to enroll, witnesses said.

“What happened is we were all gathering and … (the bomber) exploded right next to all of the police college classmates,” eyewitness Jamil al-Khaleedi told The Associated Press. “It went off among all of them, and they flew through the air.”

No one immediately claimed responsibility for the attack. Yemen’s local al-Qaida branch, targeted in frequent U.S. drone strikes in the country, has carried out similar attacks in the past. Washington considers al-Qaida in Yemen to be the world’s most dangerous branch of the terror network as it has been linked to several failed attacks on the U.S. homeland.

The blast comes as Shiite rebels known as Houthis have seized large areas of Yemen, including Sanaa, earlier this year. Their critics view them as a proxy for Shiite Iran, charges the rebels deny. Al-Qaida militants have targeted the rebels in bombings in the past.

Tribal leaders and Yemeni officials warn the rising power of the Houthis and backlash to drone strikes has caused al-Qaida’s Yemen branch to surge in strength and find new recruits. The Houthis’ push into largely Sunni regions of central Yemen has pitted the rebels against Sunnis, to the benefit of Sunni al-Qaida. While the group has lost prominent figures in drone strikes, the killing of members of prominent tribes in the strikes have pushed them toward the extremists.

Mideast Yemen