Police said yesterday they were treating bomb blasts by a lone attacker in Stockholm — which followed an e-mailed threat referring to Sweden’s troops in Afghanistan and to cartoons of Mohammad — as an act of terrorism.

Police stopped short of calling Saturday’s blasts, which killed the suspected bomber and wounded two people, a suicide attack. The incident follows several nervous months in Europe after a U.S. travel alert about possible attacks by militants and a failed bid by a Yemen-based al Qaeda group to use air cargo to send parcel bombs via Europe to America.