Russia, China and four central Asian countries meeting in Shanghai have signed a joint statement in support of the Anti-Ballistic Missile (ABM) Treaty, which the United States wants to scrap to make way for a missile defence shield.
The newly named Shanghai Co-operation Organisation (SCO) agreed that the 1972 treaty between the US and the former Soviet Union was the "cornerstone of global stability and disarmament", a Russian official said.
Attending the summit
The construction of the US anti-missile shield would effectively lead to the collapse of the ABM treaty, which Mr Bush says is no longer relevant to US-Russian ties and global non-proliferation.
Participants at the Shanghai summit have also signed an agreement aimed at stepping up efforts to defeat Islamic militants in Central Asia.
Correspondents say that despite US assurances that the proposed shield is aimed at containing rogue states such as Iraq and North Korea, there is strong opposition from China and Russia who have warned that it could trigger a new global arms race.
Analysts say China could try to combat the shield by building as many new missiles as possible.
The summit is against US plans for a missile defence system
Russian President Vladimir Putin met Chinese President Jiang Zemin for talks, in the first of several meetings planned between the two leaders this year.
President Putin is next due to hold his first meeting with Mr Bush in Slovenia on Saturday with the missile shield and the ABM Treaty top of the agenda.
Russian Foreign Minister Igor Ivanov told reporters in Shanghai that Russia and China regularly consulted about US missile defence plans and that their views "fully coincide".
Fighting Islamic extremism
At its meeting, the SCO signed another agreement, dubbed the Shanghai Convention, aimed at curbing "extremism, terrorism and separatism".
The organisation, originally called the Shanghai Five, was set up in 1996 to sort out lingering Sino-Russian border disputes.
It has evolved into a security mechanism aimed at combating the rise of Islamic militancy, mainly from Taleban-ruled Afghanistan.
On Thursday, Uzbekistan became the sixth member of the group, which Moscow and Beijing hope will counterbalance growing US influence.
A BBC correspondent in Moscow says the addition of Uzbekistan - where authorities are fighting one of the region's strongest rebel groups - is a logical progression.
China, with a large and restive Muslim population in its far west, is keen to stem the growth of Islamic militancy in Central Asia and prevent groups there linking up with Muslim separatists inside China.
All the countries at the summit are dealing with Muslim guerrillas to some extent, many of whom are believed to receive support from Afghanistan's militant Muslim Taleban movement.
But China and Russia also have broader ambitions to build the Shanghai group into a bulwark against American influence in Central Asia.