ZURICH (Reuters) - Prosecutors in Tokyo raided the local unit of Swiss drugmaker Novartis as part of an investigation into alleged use of manipulated data to promote its best-selling blood pressure drug Diovan, Kyodo News reported on Wednesday.

Japan's health ministry filed a criminal complaint against Novartis's local unit in January, saying it may have violated the law when it cited studies based on allegedly manipulated data.

Novartis said at the time that it had implemented corrective measures. In a brief statement on Wednesday, it said it does not comment on pending legal matters and would cooperate fully with the prosecutors' investigation.

Anyone found guilty of exaggerated advertising of drugs in Japan can be punished with up to two years in prison or a fine of as much as two million yen ($19,100), or both.

Several Japanese hospitals have stopped offering Diovan after two universities retracted papers printed in foreign medical journals on the drug's efficacy for preventing strokes and heart disease.

Japan is an important market for Novartis, accounting for around a quarter of Diovan's global sales before the scandal. Annual sales of Diovan in Japan have topped 100 billion yen ($954 million) since 2005, according to Novartis Pharma.

(Reporting by Caroline Copley in Zurich and Chang-Ran Kim in Toyko; editing by Tom Pfeiffer)