By Alexei Anishchuk
ASTANA (Reuters) - Russia won the backing of China and other members of a regional security body in criticizing U.S. plans for a missile shield, saying Wednesday that it could undermine global security.
The Shanghai Cooperation Organization (SCO), a security bloc grouping Russia, China and four ex-Soviet Central Asian states, signed a declaration warning against a unilateral build-up of missile defenses after their leaders met in the Kazakh capital.
"The unilateral and unlimited build-up of missile defense by a single state or by a narrow group of states could damage strategic stability and international security," the six members of the SCO said in the declaration.
Apart from regional heavyweights China and Russia, the SCO also includes the mostly Muslim ex-Soviet Central Asian states of Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan.
The member countries occupy three-fifths of the Eurasian land mass, a region of more than 1.5 billion people, or a quarter of the world's population. It was set up 10 years ago to promote regional stability and cooperation.
Moscow has recently stepped up criticism of U.S. plans to deploy missile defenses in Europe and has pressed for binding guarantees that the system would not weaken Russia's nuclear arsenal.
Russian President Dmitry Medvedev has threatened a new Cold War-style arms race if Moscow and Washington fail to resolve the missile defense spat.
The United States says the shield is meant to parry the developing threat of a missile attack by Iran, but Moscow says it fears the true aim is to weaken Russia.
Russia and China have improved relations, after a near war in past decades, and as permanent members of the U.N. Security Council the two states have expressed opposition to Western-led resolutions, including the recent condemning of Syria's bloody crackdown on anti-government protests.
China and Russia have reluctantly supported four rounds of U.N. sanctions against Iran over its nuclear program.
(Additional reporting by Dmitry Solovyov; Editing by Alistair Lyon)