At least 70 people - mostly women and children - have been killed at a crowded park in Pakistan in a suicide blast that also wounded more than 300 people, officials said.

A faction of the Pakistani Taliban, Jamaat-ul-Ahrar, later claimed responsibility for the attack in the eastern city of Lahore and said that it was aimed at Christians.

Al Jazeera's Kamal Hyder, reporting from the capital, Islamabad, said Christians were celebrating Easter Sunday at Gulshan-e-Iqbal Park, which is popular with families, when the bomber blew himself up a few metres from a children's play area.

On Monday, authorities said they would launch a manhunt for those behind the attack after Jamaat-ul-Ahrar issued a direct challenge to the government.

"We want to send this message to Prime Minister Nawaz Sharif that we have entered Lahore," a spokesman, Ehsanullah Ehsan, said. "He can do what he wants but he won't be able to stop us. Our suicide bombers will continue these attacks."

IN PICTURES: Bomb blast in Pakistan's Lahore

The group claimed responsibility for several big attacks after it split with the main Pakistan Taliban in 2014. It declared allegiance to the Islamic State of Iraq and the Levant but later said it was rejoining the Taliban campaign.

"We must bring the killers of our innocent brothers, sisters and children to justice and will never allow these savage inhumans to overrun our life and liberty," military spokesman Asim Bajwa said on Twitter.

TV footage showed children and women standing in pools of blood outside the park, crying and screaming as rescue workers, officials, police and bystanders carried injured people to ambulances and private cars.

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The bodies of those killed continued to arrive at the city's hospital morgues early on Monday, where worried friends and family also looked for and registered loved ones still missing. But local media reported that many of the bodies were being kept in hospital wards as morgues became overcrowded.

"I was a few blocks away from the blast," witness Mian Ashraf told Al Jazeera. "Many people were running and screaming like the world had collapsed. Until when will we see our loved ones getting killed in such attacks?"

Other witnesses said they saw body parts strewn across the ground once the dust had settled after the blast.

"When the blast occurred, the flames were so high they reached above the trees, and I saw bodies flying in the air," said Hasan Imran, 30, a resident who had gone to the park for a walk.

String of attacks

In 2014, Pakistan launched an offensive against the Taliban and affiliated groups in the North Waziristan region, seeking to deprive them of safe havens from which to launch attacks in both Pakistan and Afghanistan.

Lahore is the capital of Punjab, which has normally been more peaceful than other parts of Pakistan.

Last year, a bomb killed a popular provincial minister and at least eight others when it destroyed his home in the region.

Earlier this month, an explosion on a bus carrying government officials in the north of the country killed at least 15 people.

And a suicide bomber killed 13 people on March 8 after blowing himself up outside a court in Charsadda, in Khyber Pakhtunkhwa province, about 30km from Peshawar.

Soon after Sunday's attack, the Punjab government ordered all public parks closed and declared three days of mourning. The main shopping areas were closed and many of the city's roads were deserted.

"We were just here to have a nice evening and enjoy the weather," Nasreen Bibi told the Reuters news agency at the Services Hospital, crying as she waited for doctors to update her on the condition of her two-year-old wounded daughter.

"May God shower his wrath upon these attackers. What kind of people target little children in a park?"