A grenade attack in Pakistan's Karachi city on Friday left at least three policemen and a passerby injured, media reports said.

Counter-Terrorism Department Senior Superintendent of Police (SSP) Irfan Ali Bahadur told Dawn.com that police were treating the attack as an act of terrorism.

No group has claimed responsibility for the incident so far.

“An initial probe suggested that the suspects threw a grenade from the bridge, which landed in the police camp,” the SSP said.

Malir SSP Kashif Abbasi told Dawn News that in a statement that two personnel of the Police Qaumi Razakars and a Special Security Unit member were among the injured.

“One passerby was also hurt,” Abbasi was quoted as saying. “An investigation has been initiated,” he said.