Vladimir Putin revealed Russia has been working with China (Library picture: PA).
Russian President Vladimir Putin has said Moscow is helping China build a warning system for ballistic missile launches.
Only the United States and Russia have systems like these since the Cold War - the technology features an array of ground-based radars and space satellites.
The system is essential for the early detection of intercontinental ballistic missiles, similar to the Minuteman III missile which the US test-fired fired from Vandenberg Air Force Base this week.
Speaking at an international affairs conference, Mr Putin said Russia has been helping China develop such a system.
This signals a new level of defence co-operation between the two former Communist rivals, which comes as relations between Washington and Beijing have been reduced to trade wars.
Mr Putin said "this is a very serious thing that will radically enhance China's defence capability".