The two parties were also ordered to pay 4.5 million euros between them to United Arab Emirates club Al Nasr after the Court of Arbitration for Sport (CAS) said in a statement it had upheld a FIFA ruling.
CAS also rejected an appeal from Al Nasr that the compensation be increased.
FIFA said in February that Bangoura had been found guilty of "an unjustified breach of contract" after he left Dubai-based Al Nasr to join Nantes one year earlier.
Bangoura, who previously played for Dynamo Kiev and Stade Rennes, joined Al Nasr on a four-year contract in September 2010.
At the start of 2012, he went to play at the African Nations Cup with the club's permission but lost his place in the side after they signed another player to replace him.
He joined Nantes, who were in the French second division at the time, and was loaned to Qatari-side Umm Salal in September.
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