BRUSSELS (Reuters) - The European Union executive sent a formal letter to Hungary on Wednesday, officials said, the first step of a fresh offensive to safeguard democratic checks and balances that could freeze funds for Prime Minister Viktor Orban over corruption.

       Despite years of criticism by rights campaigners that he was channeling EU funds to his associates, Orban won a fourth consecutive election victory earlier this month. The European Commission responded by launching its new sanction tool.

       "We identified issues that might be breaching the rule of law in Hungary and affect the EU budget," said a deputy head of the Brussels-based Commission, Vera Jourova.

       "Hungary will have to reply to our concerns and propose remedial measures."

       (Reporting by Gabriela Baczynska; Editing by John Chalmers)