LAGOS, Nigeria (AP) — The Nigerian military said Monday that a new operation with U.S. forces has killed more than 20 Islamic State group militants in northeastern Borno state.

The operation in Metele followed the weekend killing of Abu Bakr al-Mainuki, deputy leader of the group’s local West African “province,” marking a new development in the military cooperation. It was the first successful targeting of a senior militant leader by Nigeria’s security forces after well over a decade of insurgency by armed groups including Boko Haram.

The U.S. military said no U.S. or Nigerian forces were harmed in Sunday’s strikes in the community near the borders with both Niger and Chad.

Nigerian military spokesperson Samaila Uba said efforts “in close coordination” with the U.S. military were ongoing to “disrupt terrorist networks, remove them from the battlefield and deny the terrorists any safe haven within Nigeria.”

The U.S. and Nigeria entered a military cooperation last year following a diplomatic row after U.S. officials asserted that a “Christian genocide” was occurring in the country that’s largely divided between Christians in the south and Muslims in the north. Nigeria’s government rejected the accusation, and analysts said it simplifies a complicated situation in which people are often targeted regardless of their faith.

In February, the U.S. sent troops to Nigeria in what was deemed a mostly advisory and training role, but analysts say the weekend operation showed the cooperation has advanced to active U.S. involvement.

Nigeria’s military has long used airstrikes against militants in the escalating security crisis, sometimes hitting civilian populations with devastating consequences. Earlier this month, Amnesty International accused the military of killing 100 civilians at a market while targeting militants. The military denied it.