Medan (Agencies) – A strong explosion rocked the back parking lot of mayoralty building here on Monday, injuring one people, agencies reported.

Antara reported the blast in late afternoon damaged two cars and injured a staff of the city administration. The blast came from a bomb which was laid down at a bicycle in the parking lot.

The cause of the explosion had yet to be determined and the police anti-bomb squad were at the scene, El Shinta Radio reported.

National police spokesman Edward Aritonang said officers found pieces of metal believed to be shrapnel. "This is an act of terror and aimed at creating restlessness," North Sumatra governor Rizal Nurdin was quoted by AFP.

"Maybe [the perpetrators] are not satisfied with government policies. Many people can assemble explosives now," he said.