The United States and South Korea said on Friday that the Terminal High Altitude Area Defense (THAAD) anti-missile system will be used to counter North Korea's growing nuclear and ballistic missile capabilities.
The announcement was the latest move by the allies against the North, which conducted its fourth nuclear test this year and launched a long-range rocket, resulting in tough new UN sanctions.
"There will be physical response measures from us as soon as the location and time that the invasionary tool for US world supremacy, THAAD, will be brought into South Korea are confirmed," the North's military said in a statement reported by Reuters.
"It is the unwavering will of our army to deal a ruthless retaliatory strike and turn (the South) into a sea of fire and a pile of ashes the moment we have an order to carry it out," the statement carried by the official KCNA news agency said.
The North frequently threatens to attack the South and US interests in Asia and the Pacific.
The move to deploy the THAAD system, which drew a swift and sharp protest from China, came a day after the US Treasury Department blacklisted leader North Korean leader Kim Jong Un for human rights abuses.
North Korea called the blacklisting "a declaration of war" and vowed a tough response.
South Korean President Park Geun-hye said on Monday the THAAD system was not intended to target any third country but was purely aimed at countering the threat from the North, in an apparent message to Beijing.