At least 21 people were killed and dozens wounded on Tuesday when a Taliban suicide bomber on a motorbike crashed into the main gate of a government office in the northwest Pakistan town of Mardan, officials said.

The blast highlights the Pakistani Taliban's continued ability to carry out attacks despite a major military offensive against its headquarters that analysts say has reduced the group's capacity.

"It was a suicide bomber riding on a motorbike," Faisal Shahzad, district police chief told AFP, placing the number of dead at 21 and wounded at 63.