The European Commission on Tuesday launched a probe into whether the operator of Aarhus Airport in Denmark, granted state aid to some airlines through discriminatory rebates on airport charges.

The investigation follows a complaint that airport charges set by Aarhus might constitute state aid to low-cost airline Ryanair.

"With today's decision, the Commission is opening a formal investigation procedure on possible state aid to the various air carriers operating at Aarhus Airport, including, but not limited to, Ryanair," the Commission said in a statement.