The German anti-trust authority, the Federal Cartel Office, said Tuesday it was probing five regional gas suppliers, including units of power giants RWE, E.ON and EnBW, on suspicion they set inappropriately high gas prices. The companies under investigation were Thüga, which is controlled by E.ON, RWE unit MITGAS, EnBW OstWürttemberg Donau, MVV Energie and SWU Energie, which were among the most expensive gas suppliers in the country, the competition watchdog said in a statement. The authority had demanded detailed information from the companies concerned with a view to ascertaining whether recent price increases were justified. The cartel office did not rule out widening its investigation to include other companies. Cartel office chief Ulf Böge had already said in a newspaper interview on Monday that a number of gas suppliers were under suspicion of passing on increases in oil prices to customers, but not any declines in prices.