An American journalist being held by pro-Kremlin separatists in the eastern Ukrainian town of Slavyansk will be freed soon, the local rebel chief said Thursday. Simon Ostrovsky, a reporter for the US online outlet VICE News, "will be freed as soon as possible -- you can meet him then," the self-styled rebel mayor of the town, Vyacheslav Ponomaryov told a news conference. The US government has expressed concern over the detention of Ostrovsky, who was grabbed early this week, and called on Russia to organise his immediate release.