Ukraine's security service has said the OSCE observers being held by pro-Russian forces are meant to be used as a "human shield".
The observers are being held in humane conditions, but one of them requires urgent medial attention, said the Ukraine security service.
Ukraine says the separatists holding the media freedom observers are "co-ordinating their activities with Russia", claiming that the detention was planned and run by a Russian citizen who Kiev says is a Russian special service operative.
Russia denies that it has any of its troops or agents in eastern Ukraine.
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