The Association of Southeast Asian Nations (ASEAN) has agreed to deepen engagement with Washington and Moscow by expanding the 16-nation East Asia Summit (EAS) to a "10 plus 8" dialogue, according to a joint declaration during the ASEAN foreign ministers' meeting in Vietnam on July 20.

This surprising development has attracted widespread attention.

That the US and Russia have proposed to join the EAS - and ASEAN's affirmative response to their request - was an inevitable outcome of moves to maintain balance of power and preserve the core interests of major nations in the region.

At present, ASEAN is playing a leading role in East Asian cooperation, as well as in the EAS mechanism. Though ASEAN members have different priorities in promoting East Asian cooperation, there is consensus regarding balancing diplomacy among the key powers within the region and those external powers with strategic interest in East Asia.

In recent years, the most significant change in the power balance in East Asia has been China's fast growing economy and increasing military strength. As a consequence, the "China threat" bogey has become quite entrenched in Southeast Asia.

By admitting into the EAS both the US and Russia, ASEAN aims to achieve diplomatic parity among key powers. Deepening engagement with the US and Russia would help counterbalance the dominance of rising regional powers, a Southeast Asian diplomat once said.

Singapore too has often expressed the view that the US should play an indispensable role in the Asia-Pacific region for a long time to come.

ASEAN's overtures to Washington coincide with the US initiative to return to East Asia. The Obama administration has sought to cozy up to Southeast Asian nations that had felt neglected during former President George W Bush's tenure.

US Secretary of State Hillary Clinton attended the 16th ASEAN Regional Forum and signed the Treaty of Amity and Cooperation in Southeast Asia. Clinton also proposed to set up a new "US-Mekong cooperation" framework with Vietnam, Laos, Cambodia and Thailand in the Mekong River region.

Besides participating in the ASEAN Regional Forum, which includes only the foreign ministers of 10 ASEAN member countries, the US has no involvement at all with other East Asian cooperation mechanisms.

Therefore, during his trip to Tokyo last year, US President Barack Obama promised broader engagement with Asia and to participate fully in appropriate organizational mechanisms. As the world's only superpower, the US doesn't want to be excluded from any regional cooperation mechanism, especially in East Asia.

With the establishment of the China-ASEAN free trade area, China's influence in Southeast Asia is on the rise and two-way economic contacts have gained new momentum.