MOSCOW, Sept 23 (Reuters) - Mark Gyetvay, a deputy head of Russian natural gas producer Novatek (NVTK.MM), has been arrested in the United States on tax charges related to $93 million hidden in offshore accounts, the Department of Justice said on Thursday. It said a federal grand jury in Fort Myers, Florida, returned an indictment on Wednesday charging Gyetvay, a Florida businessman, with defrauding the United States. Gyetvay holds passports from both the United States and Russia. According to the indictment, from 2005 to 2016, Gyetvay allegedly engaged in a scheme to defraud the United States by concealing his ownership and control over substantial offshore assets and by failing to file and pay taxes on millions of dollars of income. Gyetvay, who sat on the board of Novatek"s directors and was its chief financial officer from 2003 to 2014, did not return phone calls. Novatek declined to comment. Beginning in 2005, Gyetvay allegedly opened the first of two different Swiss bank accounts to hold these assets, which at one point had an aggregate value of over $93 million, the Department of Justice said. Gyetvay was appointed Novatek"s deputy head of management board in July 2010. He was scheduled to appear in court on Thursday before U.S. Magistrate Judge Douglas Frazier of the U.S. District Court for the Middle District of Florida. He faces a lengthy prison sentence if convicted of the charges.