The Shanghai Cooperation Organization (SCO) on Friday, for the first time in its history, approved the legal basis for the admission of new member states, clearing the way for more Asian countries to join the emerging bloc.

Although some experts expect the SCO to develop into a group similar to the European Union, most believe it will remain prudent on expansion to maintain efficiency.

Heads of state of China, Russia, Kazakhstan, Tajikistan and Uzbekistan, as well as delegates from Kyrgyzstan, agreed the move at an annual summit in the Uzbek capital, Tashkent.

Muratbek Imanaliyev, secretary-general of the SCO, told Russian media the legal document would define those countries that can be classed as nation applicants, which can aspire to full membership of the SCO after completing the necessary formalities.

The expansion of the organization, which covers 60 percent of the total territories of Euro-Asia and includes a quarter of the world's population, is a hot topic.

Observer nations such as India, Pakistan and Iran have expressed intentions to join the SCO, which means the bloc embracing China, Russia and Central Asian nations will possibly be expanded to South Asia and the Middle East. Many other countries in the region, including Afghanistan, have made similar appeals.

However, Iran's path was blocked on Thursday when a fourth round of United Nations sanctions fell on Teheran for its nuclear activities. The SCO has stated any country under UN sanctions cannot be admitted.

Iranian President Mahmoud Ahmadinejad did not attend the summit.

Elena Ponomareva, of the Moscow Institute of International Relations, saw the acceptance of new members by the SCO in a positive light.

"The body is entering a new phase, transforming into not only a regional outfit, but also a supra-national one that can compete with such bodies as the EU in the future," Ponomareva told Voice of Russia.

"The enlargement of the SCO will boost its economic potential, and consequently, its political influence in the world," she added.

However, President Hu Jintao told his Russian counterpart Dmitry Medvedev on Thursday that SCO cooperation and exchange with outside countries should be done in a proper and stable manner, and on the basis of improving the strength of the bloc.

Zhang Xiao, deputy director-general of the Foreign Ministry's department of European and Central Asian affairs, said on Friday that the legal basis is the first step for expanding SCO membership, noting that there are a slate of regulations to be approved on that.

"Only after the approval of those documents can member countries sit down to discuss which countries can join," he told a press briefing.

Pang Zhongying, a senior expert on world politics with Renmin University of China, is also conservative on the expansion.

"For a regional bloc, it is definitely not the more the better," he said. "Now the European Union has 27 members and we can see more complex problems. The same reason also resulted in a loose APEC (Asia-Pacific Economic Cooperation forum).

"One of the approaches to ruin a bloc is encouraging it to admit more members," he said.

That is why the SCO has been very prudent in selecting new members, added Pang. "The SCO will enroll some new members, but I don't think it will take unqualified applicants in the future."

Beijing-based 21st Century Business Herald, a leading business newspaper in China, also cited the escalating dispute between Uzbekistan and Tajikistan on water resources, which nearly delayed the Tashkent summit, as an indication of the problems that could result from an expanded bloc.

So far, the main task of the SCO has been solving internal conflicts of the countries "living here", said the analysis. "Blind expansion will spoil it with excessive enthusiasm."