A suicide bomber blew himself up at a busy police station in Indonesia’s third-largest city, wounding at least six people.

The attack came during a counterterrorism crackdown and as authorities were on heightened alert for possible attacks against police and places of worship following a militant attack last month.

National Police spokesman Muhammad Iqbal said the man passed through a guard post and into the station’s yard, which was packed with people who were lining up to get various police certificates.