Eleven Nigerian soldiers remain in Burkina Faso days after their military plane made an 'unauthorised' landing in Bobo Dioulasso. Burkinabé officials told the BBC the troops were released and allowed to return to Nigeria. But Nigerian officials say the issue is not yet settled. Kimiebi Ebienfa, spokesperson for Nigeria's foreign ministry, told the Punch newspaper that the Nigerian embassy in Ouagadougou is "engaging with the host authorities to secure their release." The incident started on Monday when a Nigerian C-130 military cargo plane flying from Lagos to Portugal was forced to land in Burkina Faso. The Burkinabé authorities called the landing an "unfriendly act carried out in defiance of international law." Nigeria's air force said technical problems forced the plane to land at the nearest airport, following safety rules and international protocols. They added the Burkinabé treated the crew well and that plans were ongoing to continue the mission. The sudden landing raised conspiracy theories, especially since it occurred just one day after Nigerian troops helped stop a coup attempt in Benin, a country bordering both Nigeria and Burkina Faso. Burkina Faso is part of the Alliance of Sahel States (AES) with Mali and Niger. The AES left the larger ECOWAS regional group in January, forming a separate military alliance as they shifted from traditional local and international ties.