UN Secretary-General Ban Ki-moon has condemned a "terrorist bombing" at a hospital in Pakistan, saying it was "particularly appalling" that the suicide attack targeted a group of mourners.
The bomber struck a crowd of about 200 people gathered at the Civil Hospital in Quetta after the fatal shooting of a senior local lawyer earlier in the day.
At least 70 people died and more than 100 were wounded in the attack in the province of Baluchistan.
"The targeting of mourners at a civilian hospital makes the attack particularly appalling," said Mr Ban's spokesman Farhan Haq.
Mr Ban urged the Pakistani government to do its utmost to bring those behind the attack to justice.
The bomber struck as more than 100 mourners, mostly lawyers and journalists, crowded into the emergency department to accompany the body of a prominent lawyer, who had been shot and killed in the city earlier in the day.
The so-called Islamic State group this evening claimed responsibility for the suicide bombing, the group's Amaq news agency reported.
"A martyr from the Islamic State detonated his explosive belt at a gathering of justice ministry employees and Pakistani policemen in the city of Quetta," Amaq said.
The Pakistani Taliban faction Jamaat-ur-Ahrar earlier claimed responsibility for the attack, but it is believed to have claimed responsibility for attacks in the past that it was not involved in.
Television footage showed scenes of chaos, with panicked people fleeing through debris as smoke filled the hospital corridors.
The motive behind the attack was unclear, but several lawyers have been targeted during a recent spate of killings in Quetta.
The latest victim was shot and killed while on his way to the city's main court complex, a senior police official said.
He was the president of Baluchistan Bar Association.
The subsequent suicide attack appeared to target his mourners, a spokesman for the Baluchistan government said.
Police cordoned off the hospital following the blast.
Aside from a long-running separatist insurgency, and sectarian tensions, Baluchistan also suffers from rising crime.
Quetta has also long been regarded as a base for the Afghan Taliban, whose leadership has regularly held meetings there in the past.
In May, Afghan Taliban leader Mullah Akhtar Mansour was killed by a US drone strike while travelling to Quetta from the Pakistan-Iran border.