A suicide bomber blew himself up outside a police academy in the Yemeni capital of Sanaa yesterday, killing at least 22 people.

Investigators said the incident bore the hallmarks of an al Qaeda operation.

Policeman Fadel Ali said police cadets were leaving the college when the bomber attacked, saying: "We ran to the place and found dozens of cadets covered in blood. The scene was horrific."

Another witness said he saw a man in his 20s enter the crowd as cadets gathered near the academy. He said: "A loud explosion shook the area and I saw cadets on the ground."

The bombing in Sanaa followed a similar attack in the capital in May, when a suicide bomber in army uniform killed more than 90 people during a rehearsal for a military parade.

Theodore Karasik, director of research and development at the Institute for Near East and Gulf Military Analysis, said al Qaeda appeared to be adopting methods used in Iraq.