WASHINGTON: The US and South Korea will deploy the advanced Terminal High Altitude Area Defence (THAAD) missile defence system on the volatile Korean peninsula as a "defencive measure" to counter the growing security threat from North Korea's weapons of mass destruction, the Pentagon said.

The deployment of the THAAD anti-missile system was taken jointly by the US and South Korea, the Pentagon said in a late night statement.

The two countries made an alliance decision to deploy THAAD to US Forces Korea (USFK) as a "defencive measure to ensure the security" of South Korea and its people, and to protect alliance military forces from North Korea's weapons of mass destruction and ballistic missile threats, it said.

They began talks in February when North Korea launched a long-range rocket after a fourth nuclear test in January. The two allies are working closely to ensure its swift deployment.

The THAAD deployment will contribute to a layered missile defence that will enhance the alliance's existing missile defence capabilities against the North's missile threats.

"When the THAAD system is deployed to the Korean Peninsula, it will be focused solely on North Korean nuclear and missile threats and would not be directed towards any third party nations," the Pentagon said.

"North Korea's nuclear test and multiple ballistic missile tests, including the recent intermediate-range ballistic missile (IRBM) launches, highlight the grave threat that North Korea poses to the security and stability of the Republic of Korea (RoK) and the entire Asia-Pacific region, it said.

Th Pentagon said that following the review that began in February, a joint working group confirmed the military effectiveness of THAAD on the Korean peninsula.

The Pentagon did not disclose when the system would be deployed, saying the two nations were in the final stage of selecting a potential venue.

But the powerful defence system, which fires projectiles to destroy enemy missiles, is likely to be deployed latest by the end of 2017.

"When the THAAD system is deployed to the Korean Peninsula, it will be focused solely on North Korean nuclear and missile threats and would not be directed towards any third party nations," the Pentagon said.

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