France's Competition Authority has expressed "serious doubts" over Casino's purchase of Monoprix.

Last June, Casino agreed to purchase joint-venture partner Galeries Lafayette's 50% stake in French retailer Monoprix, ending a long-running dispute.

Monoprix has around 400 outlets under banners including Monoprix, Monop', Dailymonop and Monop'station.

The regulator says the takeover "raises competition issues making it necessary to open an in-depth phase two investigation".

It added that the takeover "strengthens Casino's market position in certain areas of Paris given the presence in these areas, alongside Monoprix and Monop' stores of other Casino retail brand outlets such as Casino, Franprix, Leaderprice."

In a statement, Casino said the phase two examination will allow it to "put forward all its arguments to the French Competition Authority".

The timeframe for the examination is 65 working days but can be extended if required.