The North Korean Army says it has final approval to launch nuclear strikes on the United States.

In a statement, it says it's informing Washington that US threats would be "smashed".

The US is moving an advanced missile system which includes interceptor missiles, to the Pacific island of Guam as a precaution.

The Pentagon said it would deploy the ballistic Terminal High Altitude Area Defence System in the coming weeks.

Pyongyang's warlike rhetoric follows new UN sanctions and joint military drills by the US and South Korea.

The US has recently made a series of high-profile flights of stealth fighters and nuclear-capable B-52 bombers over South Korea.

Officials have also confirmed that the USS John McCain, an Aegis-class destroyer capable of intercepting missiles, has been positioned off the Korean peninsula.

A second destroyer, the USS Decatur, has been sent to the region.

On Tuesday, US Secretary of State John Kerry called recent North Korean actions "dangerous" and "reckless".

China, the North's only powerful ally, said it had despatched officials on Tuesday to hold talks with ambassadors from North Korea, South Korea and the US.