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.
More top news
Donald Trump has blamed 'radical Islamic terrorism' for UK's 13% rise in crime.
Theresa May said she is "ambitious and positive" for a Brexit deal as EU leaders gave the go ahead for preparations for second phase talks.
Merseyside Police have launched an investigation after crowd trouble at Goodison Park - during which a fan appeared to attack a player.