Both Islamic State (ISIS) and the Taliban faction Jamaat-ul-Ahrar (JA) claimed credit for Monday's bombing at a hospital in the Pakistani city of Quetta that claimed at least 70 lives and left dozens injured.
Prime Minister Nawaz Sharif called for security forces to "decimate" terrorists after the blast at the Civil Hospital in the Balochistan provincial capital Quetta, which also wounded more than 100 people.
The bomber struck a crowd of some 200 people made up mainly of lawyers and journalists that had gathered to mourn the president of the Balochistan Bar Association, who was shot dead on Monday. Bilal Anwar Kasi was attacked by two unidentified gunmen as he left his home for work.
A faction of the Pakistani Taliban, Jamaat-ul-Ahrar, claimed responsibility for both the assassination of the lawyer and the blast at the hospital. A spokesman vowed it would carry out more attacks "until the imposition of an Islamic system in Pakistan".
Hours later, the Islamic State group also said it was behind the blast, which it claimed killed 200 people, the SITE monitoring agency reported.
Bomb disposal unit chief Abdul Razzaq told AFP it was a suicide attack. "The bomber had strapped some eight kilograms of explosives packed with ball bearings and shrapnel on his body," he said.
An AFP journalist was about 20 metres (70 feet) away when the bomb went off.
"There were huge black clouds and dirt," he said. "I ran back to the place and saw dead bodies scattered everywhere and many injured people crying. There were pools and pools of blood around and pieces of human bodies and flesh."
Nurses and lawyers wept as medics from inside the hospital rushed out to help dozens of injured, he said.
Pervez Masi, who was injured by pieces of flying glass, said the blast was so powerful that "we didn't know what had happened".
"So many friends were martyred," he said. "Whoever is doing this is not human, he is a beast and has no humanity."
Pakistan is grimly accustomed to atrocities after a nearly decade-long insurgency.
A military operation targeting insurgents was stepped up last year and saw the death toll from militant attacks fall to its lowest since the formation in 2007 of the umbrella Tehreek-e-Taliban Pakistan (TTP).
But analysts have warned the group is still able to carry out major attacks.
Jamaat-ul-Ahrar, part of the TTP, also said it was behind the deadliest attack in Pakistan so far this year, a bombing in a crowded Lahore park that killed 75 people on Easter Sunday.
The group has claimed responsibility for other suicide blasts, attacks on teams carrying out polio vaccinations and called for jihad in Myanmar.
Middle Eastern jihadist group IS has been scrabbling for purchase in Pakistan, largely due to competition from well established extremist groups such as the Taliban.
Balochistan, which borders Iran and Afghanistan, has major oil and gas resources, but is afflicted by Islamist militancy, sectarian violence between Sunni and Shiite Muslims and a separatist insurgency.
Pakistani hospitals have been targeted by militants before, with a bomb killing 13 at a Karachi hospital in 2010.
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