A pair of suicide bombings on Tuesday killed more than two dozen people worshipping at a mosque in the small town of Mubi, in northeastern Nigeria.
Dozens more were injured in the attack, which came just one day after Nigerian President Muhammadu Buhari made a state visit to the U.S.
Police put the death toll at 28, The Associated Press reports, but local hospital officials and rescue workers tell Agence France-Presse that the total could be far higher.
So far, no group has claimed responsibility for the attack, but it reportedly bears the hallmarks of the Boko Haram extremist group.
The first explosion occurred at the mosque around 1 p.m., Reuters says. A witness told AFP that the bomb was set off "five minutes before the prayer started," by a suicide bomber who had joined the worshippers gathered at the mosque.
The second blast hit a few hundred yards away, as survivors were fleeing. Many of the victims were caught in that second explosion, the AP says.
The Long War Journal says the attacks "fit the modus operandi of ... Boko Haram. The faction has a long history of deliberately targeting civilians."
This is the second time in less than six months that a mosque in Mubi has been targeted by suicide bombers, killing dozens of people.
In November, more than 50 people were killed in an explosion just as morning prayers were beginning. Boko Haram is believed to be behind that attack, as well.
Mubi is located in Adamawa state, which was taken over by Boko Haram in 2014. But the extremists "were pushed out of the areas under their control by early 2015 in a concerted offensive by the Nigerian military, backed by troops from neighboring countries," as NPR's Ofeibea Quist-Arcton reported last fall.
President Buhari announced the "final crushing" of Boko Haram in December 2016, saying the extremists were on the run with nowhere to hide.
But attacks have continued.
A month ago in neighboring Borno state, militants staged an attack in the city of Maiduguri and killed more than a dozen people. That attack is also attributed to Boko Haram.
And last week, six people died when Boko Haram militants using guns and improvised explosive devices carried out an attack in Maiduguri.