A suicide bomber attacked a mosque in Afghanistan's northeastern Kunduz province today, killing scores of worshippers in the country's third attack this week on a religious institution.
Islamic State claimed responsibility for an attack that state-run Bakhtar news agency said had killed 46 people and wounded 143.
Two health officials told Reuters the death toll could be between 70 and 80.
Video footage showed bodies surrounded by debris inside the mosque, which is used by the minority Shia Muslim community.
The United Nations' local mission said the blast was art of a "disturbing pattern" of violence.
It follows others in recent days at a mosque in Kabul and a religious school in the eastern province of Khost.
There have been other similar attacks in recent weeks, some of which have also been claimed by Islamic State, whose fighters are Sunni Muslims.
The attacks underscore security challenges facing the Taliban, which took over the country in August and have since carried out operations against IS cells in Kabul.
Residents of Kunduz, the capital of a province of the same name, said the blast hit a Shia mosque during Friday prayers, the most important of the week for Muslims.
Zalmai Alokzai, a local businessman who rushed to Kunduz Provincial Hospital to check whether doctors needed blood donations, described horrific scenes.
"Ambulances were going back to the incident scene to carry the dead," he said.
An international aid worker at the MSF hospital in the city told AFP there were fears the death toll could rise.
"Hundreds of people are gathered at the main gate of the hospital and crying for their relatives but armed Taliban guys are trying to prevent gatherings in case another explosion is planned," he said.
Pictures on social media showed plumes of smoke rising into the air over Kunduz.
A video showed men shepherding people, including women and children, away from the scene. Frightened crowds thronged the streets.
Aminullah, an eyewitness whose brother was at the mosque, said: "After I heard the explosion, I called my brother but he did not pick up.
"I walked towards the mosque and found my brother wounded and faint. We immediately took him to the MSF hospital."
A female teacher in Kunduz said the blast happened near her house, and several of her neighbours were killed. "It was a very terrifying incident," she said.
"Many of our neighbours have been killed and wounded. "A 16-year-old neighbour was killed. They couldn't find half of his body. Another neighbour who was 24 was killed as well."
Kunduz's location makes it a key transit point for economic and trade exchanges with Tajikistan.
It was the scene of fierce battles as the Taliban fought their way back into power this year.
Often targeted by Sunni extremists, Shia Muslims have suffered some of Afghanistan's most violent assaults, with rallies bombed, hospitals targeted and commuters ambushed.
They make up roughly 20% of the Afghan population. Many of them are Hazara, an ethnic group that has been heavily persecuted in Afghanistan for decades.
