Story highlights THAAD missile defense part of US-South Korean attack plan, North says

US defense chief promises "effective and overwhelming" response if North uses nuclear weapons

(CNN) The commitment of the US and South Korea to a new missile defense system is pushing the Korean peninsula to the "brink of a nuclear war," North Korea warned Friday.

Pyongyang said the missile system, also opposed by China, was part of a joint plot between Seoul and Washington to mount a "preemptive attack on the North", according to a statement on the official KCNA news agency attributed to the National Peace Committee of Korea.

The statement coincided with a a visit by new US Defense Secretary James Mattis to Seoul, where he pledged to deploy THAAD -- the Terminal High Altitude Area Defense system -- to protect US and South Korean troops.

Mattis promised an "overwhelming" response to any attack mounted by North Korea.

"North Korea continues to launch missiles, develop its nuclear weapons program and engage in threatening rhetoric and behavior," Mattis said at a press conference in Seoul on Friday.

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