PESHAWAR, Pakistan — A gruesome suicide bombing midday Monday left at least 70 people dead outside a hospital in the southwestern Pakistani city of Quetta, most of them lawyers who had rushed there to protest and mourn the earlier killing of a local bar association leader.

The Khorasan branch of the Islamic State, a regional affiliate of the Mideast-based Sunni Islamist militant group, asserted responsibility for the blast in telephone calls to journalists in Pakistan. A separate Pakistani militant splinter group, Jamaat-ul-Ahrar, issued an online statement also claiming it had carried out the bombing.

Medical officials in Quetta said late Monday afternoon that about 70 people had died in hospitals and that more than 100 others were wounded and receiving treatment. The death toll climbed throughout the day as critically wounded victims succumbed to their injuries.

Prime Minister Nawaz Sharif and Gen. Raheel Sharif, Pakistan's army commander, flew to Quetta to visit hospitalized victims. The prime minister condemned the blast, expressing his “deep grief and anguish over the loss of precious human lives,” and said he planned to convene a special security meeting to address the bombing.

The attack was the deadliest in the capital of violence-plagued Baluchistan province since 2013, when a string of bombings targeted the area's Shiite Muslim and ethnic Hazara community. One bomb that detonated in a market that February killed at least 110 people.

Monday's blast, in which officials said a bomber detonated a suicide vest, appeared timed to target the crowd of lawyers, journalists and other civilians who had gathered outside the casualty ward of the city's Civil Hospital. They were waiting for the body of Bilal Anwar Kasi, head of the Baluchistan Bar Association, which had been brought for an autopsy after Kasi was shot dead Monday on his way to court. Jamaat-ul-Ahrar claimed responsibility for his slaying.

“It seems it was a preplanned attack,” Anwar ul Haq Kakr, a spokesman for the local government, said of the hospital attack, according to Reuters.

The U.S. State Department condemned both of Monday's attacks. “Today, terrorists targeted a hospital, as well as the judiciary and the media, two of the most important pillars of every democracy,” its statement said.

U.N. Secretary-General Ban Ki-moon also denounced the bombing, emphasizing that the targeting of mourners at a civilian hospital was “particularly appalling.”

Television footage of the bomb scene showed horrific carnage, with burned and bloody bodies of black-suited lawyers flung across the hospital plaza while police and emergency crews tried to help others. Several journalists were also among the dead.

The provincial government appealed to the public to donate blood, saying local medical facilities were overwhelmed.

The provincial chief minister, Sanaullah Zehri, vowed in a statement that “we will not let terrorists and their financiers play with the peace of our province.”

Zehri charged that India's intelligence service has been behind the financing of terrorism in the troubled region. India and Pakistan are longtime neighboring adversaries and nuclear powers. But the two groups claiming to have carried out Monday's bombing are both of Pakistani militant origin and were spawned in the tribal belt bordering Pakistan and Afghanistan. The Khorasan group has official ties with the Islamic State. The Jamaat-ul-Ahrar group has also reportedly claimed allegiance to it.