The head of Monaco's government says it's investigating how an alleged vast oil corruption scandal involving a Monaco-based company long went unnoticed, even though the principality has opened up its financial sector and cracked down on tax dodging.

Monaco authorities carried out raids and questioned executives of UNAOIL this week at the request of British anti-fraud authorities. The company, reportedly suspected of paying huge bribes to secure contracts for multinational oil companies, denies wrongdoing.

First Minister Serge Telle told The Associated Press on Friday that "it interests me personally as chief of the executive to know what allowed this to happen. There are probably lessons to learn."

Telle called corruption a "plague that we must fight" and said Monaco's days as a haven for dubious financial dealing "are over."