Sweden's anti-corruption prosecutor announced Tuesday the opening of an "aggravated fraud" investigation against German automaker Volkswagen (Other OTC: VLKAF - news) , which has acknowledged rigging its vehicles for environmental emissions tests.

The investigation will examine diesel models imported to Sweden between 2009 and 2015. These models were equipped with software that minimised emissions during pollution tests, but allowed the vehicles to spew out far more nitrogen oxide while on the road.

In September, the group had indicated about 225,000 such cars had been imported to Sweden, including about 104,000 cars of the Volkswagen brand, 57,000 Audis, 28,000 Skodas, 2,000 Seats and 33,000 Volkswagen trucks.

The Swedish inquiry adds to the legal troubles that have mounted worldwide for the manufacturer since the scandal was first revealed on September 18.

A total of 11 million Volkswagens worldwide were equipped with software intended to favourably distort the emission tests.

Sweden was one of the few countries where Volkswagen beat its previous sales records in 2015, while worldwide, sales volumes fell for the first time since 2002.