Putin: Russia is helping China with missile defense system

He added that Russian involvement will give China a measure of protection which only the United States and Russia currently have. China now has only a small, Russian-made S-300 system regarded as a modest deterrent.

"We are now helping our Chinese partners to create a missile-warning system, a missile-attack warning system," Putin said at the Valdai Club foreign policy conference in Sochi on Thursday. "This is a very serious thing that will dramatically increase China's defense capability, because only the U.S. and Russia have such a system now."

He added that international strategic stability was weakened by the United States' withdrawal in August from the 1987 Intermediate-Range Nuclear Forces Treaty. The United States has accused Russia of violating the treaty, and has called for China's inclusion in a new or renewed treaty, an idea rejected by China.

While it is unclear what level of assistance China is receiving in building a new defense system, Russia's S-400 system is believed to be capable of intercepting ballistic missiles with a 2,200-mile range. An S-400 system was sold to Turkey earlier this year.