A powerful bomb exploded inside a Shiite Muslim mosque in Pakistan’s northwestern city of Peshawar, killing at least 45 worshippers and wounding some 65 others, many of them critically, police said.

The blast occurred as worshippers had collected in the Kucha Risaldar mosque in Peshawar’s old city for Friday prayers.

Ambulances rushed through congested narrow streets carrying the wounded to Lady Reading Hospital.

Peshawar police chief Muhammed Ejaz Khan said the violence started when two armed attackers opened fire on police outside the mosque.

One attacker and one policeman were killed in the gunfight, and another police official was wounded. The remaining attacker then entered the mosque and detonated a bomb.

At least 150 worshippers were inside the mosque at the time of the explosion, said witnesses.

No-one immediately claimed responsibility for the blast, but both the so-called Islamic State group (IS) and a violent Pakistani Taliban organisation have carried out similar attacks in the region, located near the border with neighbouring Afghanistan.

Witness Shayan Haider had been preparing to enter the mosque when a powerful explosion threw him to the street.

“I opened my eyes and there was dust and bodies everywhere,” he said.

At the Lady Reading Hospital Emergency department, there was chaos as doctors struggled to move the many wounded into operating theatres.

Hundreds of relatives gathered outside the emergency department, pleading for information about their loved ones.

Pakistan’s prime minister Imran Khan condemned the bombing.

In majority Sunni Muslim Pakistan, minority Shia Muslims have come under repeated attacks.

In recent months, Pakistan has experienced a broad increase of violence.

Dozens of military personnel have been killed in scores of attacks on army outposts along the border with Afghanistan.

Much has been claimed by the Pakistani Taliban, which analysts say have been emboldened by the Afghan Taliban’s return to power last August.

Pakistan has urged Afghanistan’s new rulers to handover Pakistani Taliban insurgents who have been staging their attacks from Afghanistan.

Afghanistan’s Taliban say their territory will not be used to stage attacks against anyone, but until now they have not handed over any Pakistani insurgents.