Leonic Ivashov of the Academy of Geopolitical Sciences told reporters in Moscow that the Russian nuclear doctrine, which includes tactical nuclear weapons, should also take in the states that belong to the Collective Security Treaty Organization.

"Article 4 of the (CSTO) treaty must be revised and contain a concrete definition of such assistance, clearly described in military-strategic terms," Ivashov said, the RIA Novosti news service reported.

His statements came amid a continuing disagreement over U.S. efforts to establish a missile-defense system in eastern Europe.

The CSTO was formed in 2003 and includes Russia, Armenia, Belarus, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.

Article 4 calls on the CSTO members to defend one another from acts of aggression.