Officials claimed on Sunday that a suicide bomber attacked a military truck in Pakistan’s restive northwestern province bordering Afghanistan, killing three children and three soldiers.

The mountainous frontier separating Pakistan and Afghanistan has long been a hive of militant activity, with fighters using the porous border to escape state security forces.

On Saturday evening a suicide bomber detonated in a small market near Miran Shah in North Waziristan, just 26 kilometers (16 miles) southeast of Afghanistan.

Pakistan’s army said three children aged between four and 11 years-old were killed in the “suicide blast” alongside three soldiers in the heavily militarized area.

“The bomber came by foot and blew himself up when a vehicle of security forces passed by,” a local government official told AFP on condition of anonymity.

Pakistan prime minister Shehbaz Sharif said that “murderers of innocent children are enemies of humanity and Islam”.

“We will not sit in peace until we hunt down these barbarians and those who patronise them,” he added in a statement.

The attack has not yet been claimed by any militant groups.

The Pakistani Taliban — Tehreek-e-Taliban Pakistan (TTP) — has a long history of plotting strikes in the region.

The group is responsible for some of the bloodiest chapters of recent Pakistani history.

But after a brutal massacre of nearly 150 schoolchildren in Peshawar, a 2014 military offensive crushed the movement and drove its remaining members over the border into Afghanistan.

Since the Afghan Taliban returned to power in Kabul, Islamabad has increasingly complained that it is offering safe haven to militants staging attacks on its side of the border.

However, Saturday’s blast came in the midst of a ceasefire to facilitate peace talks.

In a letter, TTP leadership had warned fighters “not to violate the decision taken by the central command”.

Separately on Sunday, police said that two Sikh shopkeepers were shot dead by two gunmen riding a motorbike in the northwestern city of Peshawar, 30 kilometers (19 miles) from the Afghan border.

“Both the men died on the spot, and the gunmen escaped,” local police head Muhammad Ijaz Khan told AFP.