MOSCOW, August 21 (RIA Novosti) - A joint exercise by member states of a post-Soviet regional security grouping will go ahead as planned, the head of the Collective Security Treaty Organization (CSTO) said on Friday.

Nikolai Bordyuzha said the first stage of what is officially billed as an integrated exercise to rehearse "the employment of collective rapid reaction forces to ensure collective security" will start on August 26 at CSTO headquarters in Moscow.

He dismissed media reports saying that the drills "are being disrupted by Minsk."

Belarus refused to sign an agreement on the creation of a collective rapid reaction force under the CSTO auspices at a summit in Moscow on June 14 over trade disagreements with Russia. Uzbekistan also opted out.

"The second stage will be held in the second half of September in Belarus, and the third in October in Kazakhstan," he said.

The CSTO comprises Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia, Uzbekistan and Tajikistan.