The Islamic State (ISIS) has claimed responsibility for Friday's attack on a Shia mosque in Pakistan's northwestern city of Peshawar that killed at least 61 people and injured another 196.

A post from ISIS-affiliated Amaq news agency said a suicide bomber trained by the militant group had carried out the attack, which struck the mosque during Friday prayers.

Peshawar police chief Mohammad Ejaz Khan said investigations were still underway.

"(The attacker) walked into Kucha Risalda Mosque during Friday prayers, he started firing indiscriminately at the police and then set off the explosives on him," Khan said.

The attack was the deadliest in Pakistan since July 2018, when a strike carried out by ISIS killed 149 people in the city of Quetta.

Pakistan's intelligence agencies had "all the information regarding the origins of where the terrorists came from & are going after them with full force," the country's Prime Minister Imran Khan said in a tweet on Friday night.

Pakistan's Shia minority has long been the target of violence by Sunni Muslim Islamist militant groups, including the Pakistani Taliban, or Tehreek-e-Taliban Pakistan.

Thousands have been killed, many of them Shia Muslims, in sectarian violence in Pakistan, according to Human Rights Watch and other monitoring groups. (CNN)

•File:Crowds mourn the death of their relatives outside a hospital following a blast at a mosque in Peshawar on Friday

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