Officials from the Tokyo Prosecution Office were searching the headquarters of Novartis Pharma KK in central Tokyo, public broadcaster NHK and other media reported. The raid came after the health ministry filed a criminal complaint against the firm, which has been under fire since a university said the data in clinical studies might have been skewed to promote the drug, Valsartan. A Novartis spokesman declined to comment on the raid. "We cannot say anything related to the investigation," the spokesman said, "but we are taking this situation extremely seriously and will continue to fully cooperate with authorities." Health Minister Norihisa Tamura has described as "extremely regrettable" the incident in which an employee of the world's number two drugmaker hid his affiliation during a medical study into the effects of the drug, which is used to lower blood pressure. The studies suggested the drug -- sold under the name Diovan in Japan and licensed for use in more than 100 countries -- had some prophylactic effect on strokes and angina. The firm used data from the studies to market its drug, playing up its supposed additional benefits. Under Japan's pharmaceutical law, anyone found guilty of exaggerated advertising can face up to two years in prison or a fine of up to two million yen ($19,500). A ministry panel of experts concluded in September that Novartis Pharma KK should be held responsible for studies at various universities that used manipulated data on the drug. Novartis has maintained that the company had no knowledge of the wrongdoing.