Analysts believe the Iranian President, whose country has observer status at the SCO along with India, Pakistan and Mongolia, decided to snub the meeting over Russia's support of new sanctions by the U.N. Security Council.

Chinese President Hu Jintao (8th L, front) attends the Shanghai Cooperation Organization (SCO) summit in Tashkent, capital of Uzbekistan, on June 11, 2010.[Ju Peng/Xinhua]

"As for Iran, it is clear that neither Russia nor China want the SCO to be in opposition to the rest of the world. The SCO leaders made it clear that a country subject to international sanctions cannot become an SCO member," Fyodor Lukyanov, Editor-in-Chief of the Russia in Global Affairs Magazine, told RIA Novosti news agency.

"Given the marked deterioration in Russian-Iranian relations, Tehran has little chance of being admitted in the near future", Lukyanov, who is also a Member of the Council on Foreign and Defense Policy, said.

Russia and China still SCO's cornerstones

All-party talks were accompanied by a series of bilateral meetings at the highest level on the sidelines of the summit.

Russian and Chinese presidents held separate talks on political contacts, cooperation in solving pressing international problems and trade and economic relations.

Medvedev and China's President Hu Jintao also exchanged views on issue for the G20 and the G8 summits, due to take place in Canada shortly.

They also spoke on humanitarian cooperation and the financial and economic situation in the world, other issues on the international agenda, including further SCO activities, the situation in Central Asian, Pakistan, the Korean Peninsula and Afghanista. The SCO is one of the most influential regional organizations in the world, being the only one that includes both Russia and China.

In Tashkent, Hu made a six-point proposal on boosting SCO cooperation, including strengthening mutual trust, stepping up counter-terrorism efforts, improving SCO institutional building and decision-making mechanism, and promoting its transparency and inclusiveness.

Afghanistan: A main concern for SCO

The narrow format talks in Tashkent focused on prospects for Afghanistan's further political development.

Because of their proximity to Afghanistan or vulnerability to Afghan-originated drug-trafficking, SCO member-states have a strong interest in stabilising the situation there. They developed a comprehensive strategic approach to this issue.

The SCO's members noted the situation in Afghanistan remained the main threat to security in the region.

"The SCO decided it can assume responsibility for the future of Afghanistan. The SCO appears to be the only organization able to take the lead in Afghanistan after the withdrawal of NATO forces," expert Lukyanov said.

He said the SCO included two regional superpowers, Russia and China, and also the countries of the region with geopolitical concerns about the situation in Afghanistan. "So the SCO is holding all the cards," Lukyanov said.

SCO leaders declared that lasting peace in Afghanistan would be only possible if all the groups within the country found a consensus.

Alexander Rar, an expert from the Russia-Eurasia Center, said on Friday: "The drug threat has been more dangerous than a threat from international terrorism. For Russia, coping with the international drug business has become the major objective now."

Afghan President Hamid Karzai attended the Tashkent summit as a guest of honour.