Authorities in Burkina Faso have released 11 Nigerian military personnel held after a cargo plane from Lagos made an “unauthorised” emergency landing in its second largest city, Bobo-Dioulasso.

The breakaway regional Association of Sahel States (AES) said on Monday that the C-130 aircraft had entered Burkina Faso’s airspace without clearance, calling it an “unfriendly act”.

Burkina Faso authorities said the two crew members and nine passengers were given permission to return to Nigeria but it remains unclear whether the aircraft was also released.

Authorities in Nigeria said on Tuesday that the plane had made an unplanned stop at the Bobo-Dioulasso airport “in accordance with standard safety procedures and international aviation protocols” due to a technical concern on its way to Portugal for a ferry mission.

Ehimen Ejodame, a spokesperson for the Nigerian air force, neither confirmed nor denied comments about authorisation, or the lack of it, to make the landing but said an investigation into the incident was continuing. He also said the soldiers had been treated well by their hosts and that plans were under way to continue the mission. On Sunday, a domestic test flight in Niger state had also crashed, with both pilots surviving.

The timing of the emergency landing on Monday intensified regional scrutiny, coming a day after Nigerian airstrikes at a military camp in neighbouring Benin, where some soldiers linked to a foiled coup were reportedly in hiding.

A spokesperson for the government in Abuja said Nigeria acted in line with protocols of the Economic Community of West African States (Ecowas), following a request from Beninese authorities after soldiers briefly seized the national broadcaster and announced the removal of President Patrice Talon.

Omar Touray, president of the Ecowas Commission has said the region is in a state of emergency, referencing the fragility of democratic institutions and security challenges facing member states.

“Events of the last few weeks have shown the imperative of serious introspection on the future of our democracy and the urgent need to invest in the security of our community,” he told the bloc’s mediation and security council during a meeting in Abuja on Tuesday.

The AES split from Ecowas in January, accusing the larger bloc of interventions after military takeovers in Burkina Faso, Mali and Niger that pushed them away from traditional western allies and closer to Russia.