A suicide bomber has killed six people in Maiduguri, northeast Nigeria.
The country's National Emergency Management Agency (NEMA) said at least 17 other people were injured and taken to hospital after the blast at a mosque during early morning prayers.
The attack was the sixth time this month that Maiduguri has been hit by suicide bombers, underscoring concerns about the safety of civilians from Boko Haram Islamists.
On October 1, a wave of suicide and bomb attacks left 10 dead in the Ajilari Cross area of the city, which was hit again on October 13, killing four.
On October 15, two suicide bombers hit a mosque in Molai, on the outskirts of Maiduguri, killing 30.
The following day, three bombers also struck just before morning prayers in nearby Umarari. Four people were killed.
Last weekend, soldiers foiled a suspected suicide bomb attack at the city's main army base, shooting dead a woman who failed to stop at a checkpoint.
Friday's attack (local time) fits into a grim pattern of targeting places of worship and the use of multiple bombers to maximise civilian casualties.
NEMA said the latest strike "was carried out by a suspected lone suicide bomber whose two accomplices escaped, when some vigilant members of the community accosted them".
It was not immediately clear if the accomplices were also carrying explosives.
Nigeria's military has claimed a series of successes against Boko Haram, recapturing territory seized by the militants last year, as well as the mass surrender of fighters.
Senior officers have characterised the increase in suicide bombings against "soft" targets as a sign of the group's desperation.
But it also raises questions about the level of security to protect civilians in urban areas, after similar recent attacks in neighbouring states and near the capital, Abuja.