At least four people were injured when a van of a sensitive government office was targeted by a suicide bomber in Pakistan's north city of Rawalpindi on Wednesday morning, officials said.

Senior House Officer Police (SHO), Basharat Abbasi, said that the suicide bomber crashed into the government office's bus when it slowed down to cross a railroad crossing at Fateh Jang road of Rawalpindi, the sister city of the country's capital Islamabad.

He said that age and identity of suicide bomber, who was on foot when he attacked the bus, have not been determined yet.

Some local media reports said that the van was carrying at least five employees including two senior officials when it came under attack.

The injured people have been shifted to a nearby hospital.

No group has claimed responsibility for the attack yet.

Police and rescue teams rushed to the blast site following the attack and threw a cordon in the area.