QUETTA - Lawyers boycotted courts and staged protests nationwide Tuesday after a horrific suicide bombing at a Quetta hospital which killed 74 people including many of their colleagues.

Shops, businesses, schools and universities in the city and several other towns in Balochistan remained closed as the government announced three days of mourning.

Police stood guard Tuesday at the Civil Hospital, where the bomb tore through a crowd of some 200 lawyers who had gathered there the previous day to mourn the fatal shooting of a colleague.

Officials said Tuesday the death toll had increased to 74, with more than 100 injured.

Both the Pakistani Taliban and the Islamic State group have asserted responsibility for the attack, though neither claim has been verified by Pakistani authorities.

The IS claim, if true, would make it the group's deadliest attack so far in Pakistan, where it has struggled for purchase.

Scores of lawyers held rallies in major cities including Islamabad, Karachi, Lahore and Quetta Tuesday.

"It's very tragic. Our seniors who were our intellectuals have been killed and may God reward them in heaven," lawyer Ghulam Muhammad told AFP in Quetta.

Soldiers patrolled near-empty streets in the city as most public transport shut down, with markets and schools closed in mourning.

In Islamabad and in Karachi, lawyers called for the authorities to protect civilians. "This is not time only for weeping and crying and for lamenting, this is a time for practical steps," said Sheikh Asmuddin in the capital.

"How weak and pathetic are these people who target hospitals, where women and children, where patients, go to get treatment?" Ashtar Ausaf Ali, Pakistan's attorney general, said on Tuesday at a protest outside the Supreme Court in the capital Islamabad.

Supreme Court Bar President Ali Zafar called for the government to do more to protect lawyers.

"Lawyers are relatively more vocal against militancy and they are fighting cases against people accused of terrorism, so it would make sense that they are being targeted," said Ali Malik, a Lahore-based lawyer.

"An attack on lawyers makes a mockery of the law enforcement agencies, it undermines the promises of the state against terrorists and breeds fear among vulnerable citizens."

The Pakistani Taliban faction that claimed the attack, Jamaat-ul-Ahrar (JuA), was formed in 2014. It also claimed responsibility for Pakistan's deadliest blast so far this year - the Lahore Easter bombing, which killed 75.

The US State Department last week designated JuA a terrorist group, calling it "a splinter group of the Tehreek-e-Taliban Pakistan (TTP)".

Hours after the JuA announcement the Islamic State group also claimed the attack.

The Middle Eastern jihadists have struggled in Pakistan due to competition from well-established extremist groups such as the Taliban.

Attacks claimed by IS in Pakistan are rare, the most significant being a 2015 bus assault in Karachi that killed 47 people.

The group has made some inroads in Afghanistan, where it has carried out attacks in the east near the border with Pakistan in a tussle for supremacy with the Afghan Taliban.

Last month IS said it carried out twin suicide bombings that left 80 people dead in Kabul, the deadliest attack in the city since 2001.

But officials denied that was a turning point for the group, saying it is under heavy pressure in its eastern strongholds from US airstrikes and an Afghan ground offensive.

Senior analyst Rahimullah Yousafzai cast doubt on both claims to the Quetta bombing, saying there was little previous evidence of either JuA or IS being active in Balochistan.

But he added that suicide bombers can strike anywhere, so "we cannot rule it out".

The claims may not be competing at all, he added, suggesting the possibility of a joint attack. "Nothing is concrete."

The security situation in Balochistan is already murky and confused.

The province, which borders Iran and Afghanistan, has major oil and gas resources but is afflicted by Islamist militancy, sectarian violence and a separatist insurgency.

Medical staff said up to 60 of those killed in Monday's bombing at a government hospital were lawyers.

On Tuesday morning, four of over one hundred people wounded, including two more lawyers, died in hospital, taking the toll to 74, said Abdul Rehman, the medical superintendent at the Civil Hospital Quetta.