An Airbus A220-300 aircraft, a new brand for the CSeries passenger jet acquired from Canada's Bombardier, flies during its unveiling in Colomiers near Toulouse, France, July 10, 2018.

shares slumped 9 percent Thursday morning on reports the company is being investigated by the U.S. Department of Justice (DOJ) for "inappropriate practices."

France's Le Monde on Thursday reported, citing anonymous sources, that the aircraft manufacturer is facing an investigation into suspicious practices that includes alleged corruption in commercial contracts between France and Kazakhstan. Airbus was not immediately available for comment when contacted by CNBC.

According to the French media outlet, the company was informed by U.S. authorities at the end of summer. The newspaper, however, didn't state where it has received this information from.

Within the last two years, the U.K.'s Serious Fraud Office (SFO) and France's National Financial Prosecutor's Office (PNF) have both opened investigations into Airbus's use of middle men to conduct plane sales.

Airbus has said it is cooperating with U.S. authorities and in close coordination with the SFO and PNF, according to Reuters.

As at 12:15 a.m. London time, shares had pared losses to sit almost 4 percent lower at 82.32 euros ($94.37). In after-hours trading shares of rival firm Boeing had risen around 0.5 percent.

The European aerospace group is undergoing a period of transition as it attempts to move on from a period of high profile management departures, bribery probes and industrial action from employees.

Airbus's plane-making boss Guillaume Faury will become group CEO in April 2019 when German-born Tom Enders steps down. Last week, the firm has also announced a strategic review to work in tandem with the change of leadership.

Airbus was formed in 1969 and celebrates its 50th Anniversary next year.