BERLIN—German police say a 28-year-old man has admitted listing his infant daughter for sale on eBay but maintains that it was meant as a joke.

The 40-day-old girl was listed on the internet auction site last week at a price of 5,000 euros ($7,200). Police in the western city of Duisburg raided the parents’ apartment and put the girl into care. They opened an investigation on suspicion of human trafficking.

Police said Monday that the father went to authorities on Friday and admitted posting the offer. He gave investigators a cellphone he used to do so.

Police have described the family as refugees, without giving further details.

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