Pro-Russian rebels said Thursday they had expelled seven US and European members of the International Rescue Committee (IRC) NGO for "spying" in the eastern Ukrainian territory under their control.

"The IRC organisation, which works under the auspices of the US international development agency, was for several months acting in an illegal manner," the separatists' self-declared ministry of security said in a statement.

The expelled staff members of the aid organisation -- US and European citizens -- were working without authorisation and "actively attempting to establish contacts with (separatist) representatives in order to obtain information on the situation and social problems," the statement said.

The government in Kiev is fighting pro-Russian separatists who have taken control of parts of two key eastern regions.

The rebels said those expelled had "under cover of providing humanitarian aid to residents," collected personal data and probed locals on their attitude towards the separatist authorities.

Seven IRC members were expelled from the separatist east into government-controlled territory and their office in the rebel-controlled city of Donetsk closed, the statement added.

The IRC made no immediate comment on the expulsions.

The rebel authorities said that eight other foreign employees of the same non-governmental group were expelled last year from eastern Ukraine, where numerous international organisations continue to operate, including the International Committee of the Red Cross and Doctors Without Borders.

The conflict in eastern Ukraine between pro-Russian rebels and Kiev forces has cost over 6,000 lives so far.