A suspected Boko Haram suicide bomb attack has killed at least 22 Muslim worshippers at a mosque in Maiduguri in north-east Nigeria.
Rescue officials said two female suicide bombers were believed to have carried out the attack, which saw 17 other people injured.
One bomber blew herself up inside the mosque and the second did so outside as survivors of the first blast tried to flee.
Umar Usman, a worshipper who avoided the blast because he was late arriving to pray, told the Associated Press: "We were just a few meters away from the mosque when a loud bang erupted and all we could see was dark smoke and bodies littered around."
Co-ordinator Abba Aji, of the civilian self-defence Vigilante Group, said the mosque was in Umarari on the outskirts of Maiduguri, the command centre for the Nigerian army's military campaign against the Boko Haram group.
The insurgency is known for its use of female suicide bombers, and several suicide bombers have blown themselves up in recent months at roadblocks near the city.
Those attacks suggest the authorities have until today been successful in keeping militants away from crowded areas.
The last major Boko Haram assault on Maiduguri took place on 28 December, when Islamists armed with rocket-propelled grenades and multiple suicide bombers attacked indiscriminately, killing at least 50 people.
According to a report from the Insitute for Economics and Peace at the end of last year, Boko Haram overtook Isis to become the deadliest insurgent group in the world in 2014.
The band of Islamists has sworn loyalty to Isis and wants to extend its writ across West Africa - yet President Muhammadu Buhari has previously described the group as "beaten".
Despite a largely successful Nigerian army offensive last year, Boko Haram continues to hold sway in the far northeast of the country and across the borders into Cameroon, Niger and Chad. Its continued ability to carry out isolated terror attacks represents an ongoing embarrassment for the government.