Forensic lab experts started to explore the site of the huge car bomb explosion outside the National Security building in Shubra el Kheima in the Greater Cairo area in the wee hours of Thursday.

A state of security alert was declared in the area and vital installations were cordoned, a security source in Qalyoubia said.

Efforts are being intensified to arrest the perpetrators, he said.

A Ministry of Interior earlier said a man car stopped the booby-trapped car in front of the building. He then fled on a motorcycle that was following him. Minutes later, the car exploded.