A pro-Russian leader said yesterday that the first team of special monitors detained in the eastern Ukrainian town of Donetsk was likely to be released soon.
The OSCE now claims a second group of its observers been held captive in nearby Severodonetsk, after losing contact with them yesterday evening.
The organisation sent the so-called special monitors to observe compliance with an international accord for de-escalating a crisis in the east of the country, where pro-Russian separatists have seized control of strategic points in several towns.
There are currently 248 international members of the OSCE's special monitoring mission in Ukraine, with another 23 due to be deployed on Friday and a target of 300 by the end of June, an OSCE spokesman said.
More top news
Watch Hollywood heartthrob Chris Pratt doing a flawless Essex accent after revealing his wife Anna Faris is the reason behind it.
It will be breezy and wet tonight as rain sweeps in from the west, meaning a miserable start to Sunday morning.
BBC Political Editor Nick Robinson has revealed Labour tried to recruit him to be Ed Miliband's spin doctor in the run-up to the election.