Nigeria, April 25 -- A series of attacks across northern Nigeria during Ramadan and Easter has raised concerns about a pattern of violence timed to coincide with major religious gatherings.

On Palm Sunday, 29 March, worshippers in Jos, Plateau State, gathered under the morning sun to mark the start of the Christian Holy Week. Hours later, gunfire tore through the area, killing between 20 and 30 people, according to local authorities and media reports.

Weeks earlier, on the night of 4 to 5 March, in Ngoshe, Borno State, families had just broken their Ramadan fast and evening prayers were beginning when gunmen stormed a military outpost, entered the community, and abducted dozens of residents, according to reporting by Daily Trust and the...