A suicide bomber killed 13 people and injured 23 in northwest Pakistan Monday, in an attack which the Taliban said was revenge for the hanging of an Islamist assassin last week.

The bomber attacked as lawyers and litigants were arriving at a court complex during the morning rush hour in the town of Shabqadar.

Senior police official Fayaz Khan said 13 people had been killed and 23 wounded after the bomber blew himself up inside the complex, with the toll confirmed by a local administration official.

The Pakistani Taliban's Jamat-ul-Ahrar faction claimed responsibility for the attack, saying it avenged the hanging of Mumtaz Qadri -- feted as a hero by Islamists after he gunned down the liberal governor of Punjab in 2011 over a call to reform the country's blasphemy law. 

Qadri was hanged on February 29 in what analysts described as a "key moment" in Pakistan's long fight against militancy, saying it demonstrated the government's resolve to uphold the rule of law rather than allow extremism to flourish.

His funeral brought up to 100,000 people on to the streets hailing him as a hero. 

Monday's blast also targeted the court complex because Pakistan's judiciary was strengthening "un-Islamic laws", Ehsanullah Ehsan, a spokesman for the Taliban, told AFP.

Local TV channels showed footage of victims being rushed to hospitals soon after the blast.

Authorities said two children and two policemen were among the dead, with senior regional police official Saeed Wazir praising the "brave" effort by officers who "sacrificed their lives". 

Authorities had earlier put the toll at eight dead and 21 injured. 

Local bar association president Shair Qadir said they had requested security after receiving threats of an attack, but no action was taken in what he called a police failure. 

Shabqadar is near the Mohmand tribal district, one of seven semi-autonomous regions bordering Afghanistan where militants from Al-Qaeda and the Taliban had established bases in the past.

Islamabad launched a military offensive in the tribal areas in 2014 that has reportedly killed thousands of militants and pushed the rest over the border to Afghanistan, resulting in improved security inside Pakistan. 

However, insurgents associated with the Pakistani Taliban occasionally carry out attacks from bases inside Afghanistan.

Shabqadar is some 30 kilometres (18 miles) west of Charsadda, where extremists attacked a university on January 20 in a rampage that left 21 dead.