An Egyptian security official said Wednesday that a suicide car bomber is suspected to have been behind the deadly explosion that targeted the police headquarters in a Nile Delta city early Tuesday morning.

The attack killed 15 people, mostly police officers, and wounded over 100. It was the deadliest bombing yet in a months-long wave of violence blamed on Islamic militants.

The official said Wednesday the investigation has shown that a bomber drove a pickup truck laden with explosives close to the police headquarters in the northern city of Mansoura, then detonated it.

The official spoke on condition of anonymity because he was not authorized to speak to the media.

Tuesday’s bombing brought down an entire section of the police headquarters, incinerated dozens of cars and police vehicles and damaged several buildings.

No one immediately claimed responsibility for the bombing, which came a day after an al-Qaeda-inspired group called on police and army personnel to desert or face death at the hands of its fighters.

Copyright 2013 The Associated Press.