Uzbekistan has suspended its participation in a Russia-dominated security pact of ex-Soviet nations, officials said Thursday, a move that reflected tensions inside the grouping.

The Collective Security Treaty Organization's spokesman, Vladimir Zainetdinov, said Thursday that it received a note from Uzbekistan declaring the suspension of its involvement in the seven-nation alliance. Zainetdinov wouldn't comment on possible motives behind the move, and Uzbek officials couldn't be reached for comment. The grouping also includes Russia, Armenia, Belarus, Kazakhstan, Kyrgyzstan and Tajikistan.

Russia has touted the CSTO as an ex-Soviet response to NATO, but the pact has remained amorphous and weakened by differences among its members. The pact members created a joint rapid reaction force that held sporadic maneuvers, but its numbers were small and its mission unclear. Uzbekistan has refrained from contributing its troops to the force in an apparent reluctance to give Russia too much clout.