MOSCOW, July 22 (Xinhua) -- Member countries of the Collective Security Treaty Organization (CSTO) kicked off a joint command-staff drill in Armenia Tuesday, Russian news agencies reported.

　　About 4,000 troops from Armenia, Russia and Tajikistan participated in the four-stage military exercise, coded Rubezh-2008. Other CSTO members will be represented by military staff from respective defense ministries.

　　The first stage of the exercise was staged in Armenia and the second will be held in Russia at the CSTO joint headquarters.

　　At the third stage, CSTO nations will conduct a military operation to protect the sovereignty and territorial integrity of an "attacked" country, and the fourth stage will see a defense operation, the Itar-Tass news agency reported.

　　"The aim of the joint Rubezh-2008 command-staff exercise is to help develop the military component of the CSTO," Artur Bagdasaryan, secretary of Armenia's National Security Council, was quoted by the RIA Novosti news agency as saying at the official opening of the exercise.

　　"The exercise allows our countries to strengthen direct ties and increase the overall level of cooperation," said Boris Gryzlov, speaker of the lower house of the Russian parliament.

　　"We will see that the members of the bloc can meet any threat to collective security with an appropriate response," he added.

　　The CSTO is a security group comprising Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia, Uzbekistan and Tajikistan.