DAKAR, Senegal (AP) — A Nigerian Air Force plane made an emergency landing in Burkina Faso late Monday due to an in-flight emergency, according to a regional alliance that called it a violation of Burkina Faso’s airspace.

The Alliance of Sahel States, which includes Burkina Faso and neighboring Mali and Niger, placed their air and anti-air defenses on maximum alert with authorization “to neutralize any aircraft that violates the confederation’s airspace,” according to a statement by Gen. Assimi Goita, leader of Mali’s military junta.

The Nigerian Air Force confirmed Tuesday that its aircraft headed to Portugal made the emergency landing in the western city of Bobo-Dioulasso, which had the nearest airfield. The nature of the emergency was not immediately disclosed.

Ehimen Ejodame, a Nigerian air force spokesman, said the landing was done in accordance with standard safety and international procedures.

“NAF crew is safe and have received cordial treatment from the host authorities,” Ejodame said in a statement.

The Sahel alliance statement said there were two crew members and nine passengers on the aircraft.

The incident follows fractured relations between the alliance and Nigeria, which was involved in intervention efforts that helped reverse a short-lived coup on Sunday in Benin, where the Nigerian Air Force conducted airstrikes targeting the coup plotters. Burkina Faso is on the northwest border of Benin and Nigeria is on Benin’s eastern border.

Nigeria is one of 15 members of West Africa’s regional bloc, the Economic Community of West African States. Burkina Faso, Mali and Niger formed the Sahel alliance after withdrawing from ECOWAS, which the alliance accuses of inhumane, coup-related sanctions and working against the interests of citizens in alliance countries.