A suicide bomber targeted worshippers who had gathered at a mosque in north Afghanistan for prayers to mark Eid al-Adha, killing at least 41 people.
More than 50 people were wounded in the attack, which happened as people were leaving the mosque in Maymana, capital of Faryab province.
Senior provincial government and police officials attended the prayers, but appeared to escape serious injury.
The victims were mainly civilians and police officers.
“We had just finished Eid al-Adha prayers and we were congratulating and hugging each other,” deputy provincial governor Abdul Satar Barez told the AFP news agency.
“Suddenly a big explosion took place and the area was full of dust and smoke and body parts of police and civilians were all over the place. It was a very powerful explosion.”
He said the provincial police chief, Abdul Khaliq Aqsai, was wounded, but it was not clear if he had been the target.
Shafi Bekoghlu, a BBC Uzbek reporter based in Maymana, said he had been due to go to the mosque but was running late so went to a different mosque for Eid prayers.
“Just as I got home, I heard a very loud explosion. I rushed to the hospital and saw lots of cars, police cars and ambulances – carrying bodies in,” he said, adding that police fired warning shots into the air to prevent people entering the hospital.
“I went back to the hospital a couple of hours later and saw the bodies of policemen lined up.”
The BBC’s Bilal Sarwary in Kabul says that security had been very tight around the mosque, and questions will now be asked as to how the attacker managed to get past at least four security checkpoints.
Mr Barez said the attacker had been wearing a police uniform, which may have helped him gain access to the area.
Attacks in northern Afghanistan are far less common than in the south and east, and Faryab province has been considered to be relatively peaceful.
However, there have been a spate of assassinations in Maymana in recent days, our correspondent says.
A senior former Taliban commander, who had defected to the government side, was killed along with son, as well as a number of very prominent tribal elders seen to be giving crucial support to the government.
Friday’s attack came as Afghan President Hamid Karzai urged the Taliban to stop “killing their people and destroying their mosques, hospitals and schools” and join the peace process.
“They can run for any position they want… if they want to join the government they are welcome,” Mr Karzai said of the insurgents in his Eid al-Adha message.
