Russian authorities have said the cause of the Russian dissident’s death is still unknown and refused to release his body for 2 weeks as the preliminary inquest continues.

National Security Council spokesman John Kirby said the U.S. had not determined how Navalny had died, but insisted that the ultimate responsibility lies with Russian President Vladimir Putin.

The Moscow City Court rejected an appeal against Gershkovich’s detention filed by his lawyers, upholding an earlier ruling to keep him behind bars until the end of March.