A suicide bomber blew himself up outside a government office in northwest Pakistan Tuesday, killing at least 22 people and injuring 45 others. Jamaat-ul-Ahrar, a splinter group of the Tehrik-e-Taliban Pakistan (TTP), claimed responsibility for the attack, Dawn, a local newspaper, reported.

The incident took place in the city of Mardan, outside the office of National Database and Registration Authority (NADRA), which issues identity cards to residents, the Associated Press (AP) reported, citing senior police officer Saeed Khan Wazir, who also also said the some of those injured were in a critical condition.

Wazir also said that although a security guard tried to stop the bomber at the gate of the office, where people had lined up to apply for a local identification card, the bomber, who was on a motorbike, rammed his vehicle into the gate and detonated his vest. However, a conflicting report said that the bomb may have been planted in a motorbike parked near the office.

Pakistani Prime Minister Nawaz Sharif condemned the attack and urged authorities to ensure the possible treatment for the injured.

Ahsanullah Ahsan, a spokesman for Jamaat-ul-Ahrar group, which split from the TTP last August after denouncing its “narrow, personal objectives,” told AP that the blast was a "noble act to punish NADRA because it extends support to security forces." 

Mardan lies about 30 miles northwest of Peshawar, where Taliban militants stormed into a military-run school and killed nearly 150 people, mostly students, last year, in an attack that elicited global condemnation.

Peshawar is also the capital of the restive Khyber Pakhtunkhwa province, located near Afghanistan, and lies adjacent to the North Waziristan region, where the country’s army began a crackdown on Taliban in 2014. The army claims to have killed about 3,500 insurgents in the region so far and says that it has received "phenomenal successes" against the group. 

According to a BBC report, the army offensive has been successful in reducing the number of major terrorist attacks in the country over the past year.