The new criminal probe concerns the activities of The Mission Continues, a veterans charity founded by Greitens in 2007, and whether it improperly coordinated with his 2015 election campaign for fundraising purposes.

It comes on top of an expanding investigation by the city prosecutor in St. Louis into Greitens, who was arrested last month after a grand jury issued a charge of criminal invasion of privacy after allegations that he blackmailed a woman with whom he was having an affair.

He is facing calls to resign from both fellow Republicans and Democrats, as well as a separate investigation by the state’s legislature which could lead to impeachment.

“The Attorney General’s Office has an open inquiry into the charitable activities of The Mission Continues,” spokeswoman Loree Anne Paradise said in a statement emailed to AFP.

The probe was connected to “consumer protection and charitable registration and reporting laws,” she said.

Greitens was criminally charged last week in connection with allegations that he took a photograph of his former mistress blindfolded, tied up and partially nude, and threatened to expose her if the affair became public.

He faces trial in May on a felony invasion of privacy charge.

The governor had admitted to the affair prior to taking office but denied any wrongdoing. He and his surrogates have also criticized the St Louis prosecutor that charged him, saying she was motivated by politics.

The Republican-led Missouri House formed a committee Monday to investigate Greitens over the allegations surrounding his affair.

Greitens’ attorney and The Mission Continues did not immediately respond to requests for comment.