Reports say at least 24 people have been killed and more than 70 wounded by a bomb that exploded at a market in Pakistan near the Afghan border.
Pakistani officials said the blast occurred as the market in the town of Parachinar was crowded with shoppers on December 13.
The militant group Lashkar-e-Jhangvi claimed responsibility for the attack.
Ali bin Sufyan, a spokesman for the banned group whose sectarian ideology is closely aligned with Islamic State militants, told Reuters by telephone on December 13 that the bombing was "revenge for the killing of Muslims" by Syrian President Bashar al-Assad's regime and by Iran.
Earlier in December, Reuters reported that a Shi'ite unit of Pakistani fighters known as the Zeinabiyoun were joining the war against Islamic State in Syria.
Many of those fighters come from Parachinar, which has a large Shi'ite population -- unusual in Sunni-majority Pakistan.
Parachinar is the main town in the Kurram tribal region, which has been a scene of violence from Islamic militants and sectarian conflict between Sunni and Shi’ite Muslims. Suicide attacks and explosions of planted bombs have killed scores in the Kurram region.
Pakistan's military has carried out regular operations in the region to eliminate militants and control sectarian strife.
A large number of people, including women, were buying warm clothes when the bomb went off around noon local time, Ali Turi, a shopkeeper, told the German news agency dpa from the area.
"It was very loud," he said, as he described the scene. "We ran out, people were screaming, and then there were bodies and blood all around."
Local television footage showed hundreds of male marketgoers fleeing the area as police tried to cordon off the location and ambulances rushed to the site.
A doctor at the main local hospital where the wounded were taken told AFP that most of them were in critical condition and that the death toll could increase.
Parachinar is the main town in the Kurram tribal region, which has been a scene of violence from Islamic militants and sectarian conflict between Sunni and Shi’ite Muslims. Suicide attacks and bomb explosions have killed scores in the Kurram region.
Pakistan's military has carried out regular operations in the region to eliminate militants and control sectarian strife.
The December 13 attack at the Parachinar market comes a day after the army said it had almost chased insurgents from the last of their mountain hideouts in nearby North Waziristan tribal district.
A Pakistani Army spokesman said on December 12 that the military had killed 3,400 Taliban rebels in the offensive launched in mid-June 2014.
