A 73-year-old American jailed by Russia as a mercenary for Ukraine protested his innocence when his U.S.-based legal team and family finally tracked him down in April, months after he vanished into the vast Russian prison system, they said.

Stephen Hubbard, a retired schoolteacher, was sentenced last October to almost seven years in a penal colony after a court found him guilty of serving in a Ukrainian territorial defence unit against Russian forces, tasked with manning a checkpoint.

The U.S. Embassy in Moscow has not been granted consular access to Hubbard, a State Department spokesperson said, adding that U.S. officials have requested his immediate release. Martin De Luca, his U.S.-based lawyer, told Reuters it was not until this April that his legal team learned Hubbard was being held in a facility in the Mordovia region, east of Moscow.