A suicide bomber set off a large blast on Wednesday, causing severe damage to the five-story General Security building in Riyadh, Saudi Arabia, according to CNN.

The bomber was killed, CNN quoted witnesses as saying.

But the exact number of casualties is not clear yet.

The building is on Al-Washim street in the Naseriah neighbourhood, which is near the information ministry and the headquarters for the security forces that guard the royal family.

TV pictures showed the entire front of the building had been shattered. There were burned-out and damaged cars too.

The blast went off at a time when the building would have been filled with workers.

The network quoted a Saudi official as saying that authorities were tipped off to six explosive devices and they could defuse five.

However, he said the sixth exploded.