A report from AFP says that the North Korean military announced they have received approval to launch a nuclear strike on the United States. Unfortunately, the North Korean military failed to mention who exactly gave the North Korean military "approval."
But don't worry, they couldn't if they tried. Calm down. Breathe.
First, most reports indicate that North Korea couldn't attack the continental United States even if they wanted to. Their long range missiles aren't powerful enough. The furthest those missiles could reach is Alaska and maybe Hawaii, if the winds strong enough.
Second, there might a possibility that North Korea has nuclear weapons, but its more likely than they don't.
Yonhap News says, "In a statement, the North's supreme military command said it is formally notifying the White House and the Pentagon that "reckless operations" involving cutting-edge nuclear weapons have been finally approved."
It seems like this is a retaliatory measure, after new Secretary of Defense Chuck Hagel announced that the US would be moving missile defense batteries to Guam, a US territory. Hagel referred to North Korea as a "clear" and "present" danger.
That being said, Business Insider writes that the US military troop movements indicate that the military is predicting some sort of missile strike on the US. The Lowry Institute for International Policy writes:
This is unacceptable. The United States, Australia, and other allies appear to be taking important policy decisions on the basis of the imminent deployment of the KN-08 [a North Korean missile]. If this is the case, they should say so directly and provide the basis for asserting the imminent deployment of the KN-08.