Franck Riester was speaking on a visit to Benin.
France promised last year to send back 26 pieces now in the Quai Branly museum in Paris without delay, but Benin said it needed time to build a proper exhibition facility.
The 26 thrones and statues were taken in 1892 during a colonial war against the then Kingdom of Dahomey.
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Their return is expected to put pressure on other former colonial powers to hand back artefacts taken during the colonial era.
During colonial rule in Africa, thousands of cultural artifacts were seized from the continent by Western countries.
An experts' report from last year states that most of the Africa collection in the Quai Branly museum - approximately 46,000 pieces - was acquired with some degree of duress.