The five other journalists were released after they were detained Monday night, but Simon Ostrovsky, a writer and producer for Vice News Network, remained in custody. No details of his condition were available.
Vice News is headquartered in Brooklyn, N.Y., and has about 25 offices worldwide.
Ostrovsky has been in Ukraine throughout the crisis there, reporting on Russia's annexation of Crimea. He was born in Ukraine.
In an interview last month, he claimed he has encountered hostility in reporting from the region, saying, “I think it’s because of the propaganda that Russia is broadcasting over the television networks, 24/7, brainwashing the people into thinking that the entire world has come out against Russia.”
A statement from Vice News said the company is in contact with the U.S. State Department, and is working to secure Ostrovsky’s release.