BEIJING (Reuters) - Chinese President Xi Jinping set off on a visit to Russia on Monday stressing the grave threat a U.S. anti-missile system in South Korea poses to both Chinese and Russian interests.

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China has repeatedly stated its opposition to the U.S. Terminal High Altitude Area Defense (THAAD) anti-missile system and has called for its deployment to stopped, and the missiles already installed to be removed.

China says the system’s powerful radar can probe deep into its territory, undermining its security and a regional balance while doing nothing to stop North Korea in its relentless pursuit of nuclear weapons and the missiles to deliver them.

“The U.S. deployment of an advanced anti-missile system in South Korea gravely harms the strategic security interests of China, Russia and other countries in the region,” China’s state Xinhua news agency cited Xi as saying.

The United States and South Korea say the THAAD is solely aimed at defending the South from North Korea.

China and Russia have maintained close communication and coordination on the issue and held very similar views on it, Xi said in an interview with Russian media.

“Beijing and Moscow are steadfastly opposed to the THAAD deployment and seriously suggest that relevant countries stop and cancel the installation,” Xinhua cited xi as saying.

China and Russia would take “necessary measures”, either together or independently, to protect their interests, Xi said, without elaborating, according to Xinhua.

Xi also said China and Russia should work together to boost trade and increase investment and financial cooperation, Xinhua reported.

Xi will arrive in Moscow for a state visit on Monday before traveling to Germany to attend a G20 summit.

Relations between China and South Korea have been strained by the THAAD deployment though both sides have struck a more conciliatory tone since President Moon Jae-in took office in South Korea May.

(This story was refiled to correct name of missile system in second paragraph)