PARIS, France - Paris prosecutors have launched a preliminary investigation into the terms of the sale of French department store chain Printemps to Qatari investors, the prosecutor's office said on Friday.

The probe, launched on June 28 and conducted by the financial police, is a potential thorn in the side of sellers Deutsche Bank and Italian businessman Maurizio Borletti.

They clinched 1.75 billion euros for Printemps earlier this week, according to a source familiar with the transaction.

Borletti and Printemps officials could not be immediately reached for comment.

Unions at Printemps had asked authorities in May to open a probe into the terms of the sale of the luxury shop chain to investors from the gas-rich Gulf state of Qatar.

Through Luxembourg-based company Divine Investments, Qatari investors bought Borletti Group's 30 percent stake in Printemps as well as the 70 percent holding owned by Deutsche Bank's real estate investment unit RREEF.

The size of the deal or the precise identity of the Qatari investors have not been officially disclosed.

France has proven attractive to Qatari investors who have bought Paris Saint-Germain football club and stakes in energy giant Total, building firm Vinci and media group Lagardere, although the investments have provoked some criticism among the French public.

Borletti and RREEF bought Printemps in 2006 from French luxury group PPR, now called Kering, for 1.1 billion euros.

Printemps now has 16 stores and employs about 4,000 staff. Its 2011/12 turnover rose 13 percent to 1.45 billion euros.