Gunmen stormed a bus in southern Pakistan and ordered its Shiite Muslim passengers to bow their heads before shooting them, killing at least 45 people in the latest attack targeting religious minority, officials said.
Who carried out the attack in the port city of Karachi wasn't immediately clear, as a Pakistani Taliban splinter group and an Islamic State affiliate both claimed the attack. However, some Taliban fighters have pledged their allegiance in recent months to the extremist group that now holds a third of Iraq and Syria in its self-declared caliphate.
"These are the people who are extremists, who are terrorists," provincial police chief Ghulam Haider Jamali said of the assailants. "These are the same people who have been doing terrorism before."
The bus was in a relatively deserted area on the outskirts of the city en route to an Ismaili Shiite community center when six gunmen boarded it, Jamali said. Investigator Khadim Hussain said the attackers ordered the passengers to bow their heads and not look up before opening fire at close range.
Shell casings at the scene suggested the gunmen used both pistols and machine guns in their attack before fleeing on three motorcycles, police said. Jamali said the attackers killed 45 people, including 16 women, and wounded 13.
Qadir Baluch, a security guard at a nearby building, said he heard the gunshots and saw at least one of the militants wearing a police uniform.
The attack riddled the bus with bullet holes, but its wounded driver still could drive it to a nearby hospital, said Mohammad Imran, a guard there.
"I hardly saw any survivor," he said.
It wasn't immediately clear who carried out the attack. Pamphlets found nearby the site of the attack claimed an Islamic State affiliate carried it out, calling it revenge for the killing of their fellow fighters in Pakistan, Syria, Iraq and Yemen, police officer Najeeb Khan said.
Khan said the pamphlet read: "We swear that we will keep on making you and your families mourn in tears of blood."
Meanwhile, a man describing himself as a spokesman for a splinter faction of the Pakistani Taliban called Jundullah, or Army of God, claimed responsibility for the attack in a call to The Associated Press. The man, who identifies himself as Ahmad Marwat and has conveyed similar claims in the past, said "infidels were the target."
The Taliban and other Sunni militant groups long have had a presence in Karachi. Sunni extremists view Shiites as apostates and have targeted them in the past, though attacks on the Ismaili branch have been rare.
Wednesday's attack was the deadliest in Pakistan since December, when Taliban militants killed 150 people, mostly young students, at an army-run school in Peshawar.
The Pakistani Taliban have been fighting for more than a decade to overthrow the government and impose a harsh version of Islamic law. Their attacks have killed tens of thousands of people.
The Islamic State group, meanwhile, has demanded the allegiance of the world's Muslims and has drawn radicals for its bloody propaganda videos, featuring mass killings or beheadings. Some in Pakistan have recreated that in their own filmed killings. A Pakistani government letter written in December and later obtained by the AP warned local officials that the Islamic State group claims the support of up to "12,000 followers" in northwest Pakistan.
This is the second time pamphlets attributed to the Islamic State group have been found at the site of an attack in Karachi, government counter terrorism officer Umar Khitab said.
The Islamic State group in the so-called "Khorasan Province," the affiliate named in the pamphlets, later posted the claim of responsibility on Twitter, according to the SITE Intelligence Group, a US firm that monitors terror groups.
Pakistani army chief Gen. Raheel Sharif cancelled a three-day visit to Sri Lanka after the attack.
"No efforts will be spared to apprehend and punish perpetrators of this terrorist act, their abettors, and backers," a statement from his office read.
Prime Minister Nawaz Sharif, who rushed to Karachi, also condemned the bus attack, calling it "an attempt to create chaos."
"Terrorists have chosen a very peaceful and patriotic community to target in order to achieve their nefarious designs," he said.
At the Karachi hospital that took in the wounded, panicked relatives wept and tried to comfort teach other. Soofia Ali, 18, who lost her parents, wailed outside an intensive care unit where her wounded brother clung to life, unable to speak to those around her. A relative consoled her, asking her to pray.