Seoul/Washington - North Korea said it had approved nuclear attack on the United States in its latest threat Thursday, as US Defence Secretary Chuck Hagel warned Pyongyang to back down

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The White House and Pentagon would be notified that "reckless operations" using nuclear weapons had been approved, North Korea’s supreme military command said in a statement quoted by South Korean news agency Yonhap.

Analysts have said North Korea is not technologically capable of carrying out a strike on the US mainland but could target US troops stationed in South Korea or Japan.

The North Korean announcement came shortly after the US said it will deploy a ballistic missile defence system on its Pacific island of Guam as part of Washington’s efforts to beef up its military presence in the region.

The land-based Terminal High Altitude Area Defense System (THAAD) "will strengthen defense capabilities for American citizens in the US territory of Guam and US forces stationed there," the Pentagon said.

Hagel called Wednesday on Pyongyang to back down from its "dangerous rhetoric."

"We take those threats seriously. We have to take those threats seriously," Hagel said at the National Defence University in Washington.//DPA