The Collective Security Treaty Organization (CSTO) on Saturday called on all 'nuclear club' members to join the Russian-U.S. efforts and contribute to the disarmament process.

The post-Soviet security bloc, which held an informal summit near Moscow, adopted a joint statement welcoming the signing of the Russian-U.S. strategic arms reduction treaty.

"The CSTO member states regard this agreement as an important element of the international security architecture, reflecting the substantial contribution made by Russia and the United States to nuclear disarmament and nonproliferation," the statement said.

The Russian-U.S. arms pact, signed on April 8, stipulates that the number of nuclear warheads is to be reduced to 1,550 on each side over seven years, while the number of delivery vehicles, both deployed and non-deployed, must not exceed 800.

The CSTO summit opened at the Russian president's Gorki residence just outside Moscow.

It was attended by Russian President Dmitry Medvedev, Armenian President Serzh Sargsyan, Belarusian President Alexander Lukashenko, Kazakh President Nursultan Nazarbayev, Tajik President Emomali Rakhmon, Uzbek Prime Minister Shavkat Mirzieyev and CSTO General Secretary Nikolai Bordyuzha.

The meeting is expected to discuss current international issues, in particular the situation in Kyrgyzstan.

The CSTO is a security grouping comprising the former Soviet republics of Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia, Uzbekistan, and Tajikistan.

Kyrgyzstan did not participate in the summit. Russian presidential aide Sergei Prikhodko said on Friday the reason was that the country had not formed its constitutional government.

The CSTO pledged humanitarian aid to Kyrgyzstan.

It adopted a joint statement, stating its readiness to provide assistance to Kyrgyzstan and promote "constructive cooperation with other countries and international organizations along these lines."

The Kyrgyz opposition took power in the former Central Asian Soviet republic in early April after anti-government protests in several cities turned violent, particularly in the capital, Bishkek.

The country's ex-president Kurmanbek Bakiyev was deposed and fled the capital taking refuge in Belarus.