A group of Pakistani Taliban claimed responsibility of the government office attack in Pakistan's northwest Mardan district that has left 21 people killed on Tuesday afternoon, local media reported.

Express News reported that the group Jamaat-ul-Ahrar, that split away from Tehreek-i-Taliban Pakistan in 2014 and rejoined it in March 2015 amid fears of isolation, took credit for the attack in a telephone call to media.

Sayyad Khan, Deputy Inspector General Police, confirmed that 18 people were killed and 47 others injured in the blast, but the latest reports by local media said that the death toll has risen to 21.

Khan said that a suicide bomber rammed his explosive-laden motorbike at the main gate of the National Database Registration

Authority (Nadra) located at Dosehra Chowk area of Mardan in the country's northwest Khyber Pakhtunkhwa province.

He said that the attacker wanted to blow himself up inside the building, but rammed his bike into the gate after a security guard stopped him for security check.

Khan added that the blast happened when a number of people were lining up inside the Nadra office for getting their National Identity Card.

The bomb disposal squad said that an estimated eight kilograms of explosive materials were used by the suicide bomber who was 22 to 23 years old.

The injured people have been shifted to District Hospital and Mardan Medical complex by the rescue teams where several of them are said to be in critical condition.

Eight seriously injured people were shifted to Khyber Pakhtunkhwa's capital city Peshawar where two of them succumbed to injuries.

The Nadra building was also damaged in the blast.

Police cordoned off the area for investigations.