​Pakistani authorities detained more than 5,000 people, then released most of them, in the two days since a suicide bomber hit a park in the eastern city of Lahore at Easter, killing at least 70 people, a provincial minister said on Tuesday.

Investigators are keeping 216 suspects in custody pending further investigation, said Rana Sanaullah, a state minister for Punjab province from Prime Minister Nawaz Sharif's ruling party.

Sanaullah said 5,221 people were initially detained, 5,005 were released after verifying their identities, and the rest have been referred for further investigation.

"After further investigation we will know more about them," he said. "If someone is found to be guilty they will be charged."

Details of the sweeping raids — aimed at anyone suspected of Islamist extremism — came as the Taliban faction claiming responsibility for the attack issued a new threat on Tuesday, singling out the media.

Deadliest attack since 2014

The Easter bombing was Pakistan's deadliest attack since a 2014 school massacre, which the Taliban took responsibility for, killed 134 students. Sunday's attack, which included 29 children among the dead, showed the militants can still cause carnage despite military raids on their northwestern strongholds.

Forensic investigators look for evidence at the site of the blast. (Mohsin Raza/Reuters)

Lahore is the capital of Punjab, Pakistan's richest and most populous province and Sharif's political heartland.

Sanaullah said at least 160 raids were carried out by a mixture of police, counterterrorism and intelligence agents and confirmed that army and paramilitary forces would be used in future operations "This operation will include all law enforcement agencies," Sanaullah said.

Government crackdown

Military and government officials on Monday said that the military was preparing to launch a new paramilitary counterterrorism crackdown in Punjab. The move, which has not yet been formally announced, represents the civilian government once again granting special powers to the military to fight Islamist militants.

Jamaat-ur-Ahrar, which also previously declared loyalty to ISIS, has carried out five major attacks in Pakistan since December.

In a televised address to the nation on Monday night, Sharif vowed to continue pursuing militants.

"I am here to renew a pledge that we are keeping count of every drop of blood of our martyrs. This account is being settled, and we will not rest till it is paid," Sharif said.

Police officers stand guard at the site of the bomb blast, which took place near children's rides. (K.M. Chuadary/Associated Press)

The government also announced that Sharif would be cancelling a planned trip to the United States to attend a nuclear security summit, due to begin on Thursday.

Pakistan's security agencies have long been accused of nurturing some Islamist militants to use for help in pursuing objectives in Afghanistan and against old rival India.

In recent years, Pakistan has cracked down on movements that target its own citizens and institutions, including the Pakistani Taliban who are fighting to topple the government and install a strict interpretation of Islamic law.

Militant threats continue

Jamaat-ur-Ahrar, the Taliban faction that claimed responsibility for the blast aimed at Christians celebrating Easter, warned Pakistani media outlets they could be the next target.

"Everyone will get their turn in this war, especially the slave Pakistani media," Ehsanullah Ehsan, spokesman for Jamaat-ur-Ahrar, tweeted. "We are just waiting for the appropriate time."

Jamaat-ul-Ahrar claims responsibility for the suicide attack 4:23

Even as authorities pursued Islamist militants across Punjab, hundreds of ultra-conservative Muslim protesters remained camped out in front of parliament on Tuesday in the capital, Islamabad, days after clashing with police.

Mobile phone networks in the capital were blocked for security purposes for a second day in a row.

"Let Nawaz Sharif know that this war has now come to the threshold of his home," tweeted Ehsan. "The winners of this war will, God willing, be the righteous mujahideen."