At least 12 people were killed and many more injured when a suicide bomber on a motorbike crashed into the main gate of a government office in the northwest Pakistan town of Mardan, officials said.

"The death toll stands at 12 now, many others are injured," District Police Chief Faisal Shahzad told AFP.

Ali Khan, a doctor at the district headquarters hospital confirmed the death toll and placed the number of injured at "more than 30".