The proposed Terminal High-Altitude Area Defense Systems to guard against North Korea missiles.
Chinese state media say Beijing and Moscow have agreed to take "further countermeasures" in response to plans for an advanced US missile defense system in South Korea.
The Xinhua News Agency says the agreement was reached during security talks between the two countries in Moscow on Thursday.
The report gave no details and a Chinese Foreign Ministry spokesman on Friday said only that China has a legitimate right to defend its security interests. The proposed Terminal High-Altitude Area Defense, or THAAD, radar system aims to guard against North Korea missiles.
China has campaigned relentlessly against the deployment, warning of unspecified retaliation and prompting a sharp downturn in relations with Seoul. China says the powerful radar system can peer deep into its territory.
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