Russia and China have condemned a US plan for a missile defence shield, saying it will set back international disarmament efforts, reported BBC.
Russian President Dmitry Medvedev signed the joint statement with Chinese President Hu Jintao while in Beijing on his first official foreign trip.
The US says the missile system is key to its own security and that of allies.
Both Russia and China have opposed the plans in the past but this is the first time they have come together to do so.
The US, which wants to locate a radar base in the Czech Republic and an interceptor missile site in Poland, says the system will offer protection against missiles fired from states like Iran.
However, the plans have soured US-Russian ties, with Moscow fearing that the system could be used against Russia.
The joint statement from Presidents Medvedev and Hu came as the Russian leader began a two-day state visit to China, part of his first foreign trip since he assumed office on 7 May.
"Both sides believe that creating a global missile defence system, including deploying such systems in certain regions of the world, or plans for such cooperation, do not help support strategic balance and stability, and harm international efforts to control arms and the non-proliferation process," it said.
"It harms the strengthening of trust between states and regional stability. In this respect [the two sides] express their concern."
The two leaders also witnessed the signing of a US$1bn (£500m) deal under which Russia will build a nuclear fuel plant in China.