Islamic State West Africa (ISWA) insurgents overran the town of Rann in northeastern Nigeria on Monday evening, security sources said, a blow to President Buhari’s efforts to defeat the militants just weeks before national elections.

Buhari came to power in 2015 on promises to defeat the Boko Haram Islamist insurgency, from which ISWA split in 2016. ISWA has since become the dominant group in Nigeria’s northeast, with a surge in attacks renewing debates around security in the run-up to elections on Feb. 16.

Nigerian government forces fled during ISWA’s attack, along with residents of the town, the sources said, adding that the militants were setting buildings ablaze.