The United States is taking "all the necessary precautions" in the face of escalating threats from North Korea, White House spokesman Jay Carney said Thursday.

"What we're seeing now is a familiar pattern of behavior... regrettable but familiar," Carney said aboard Air Force One as President Barack Obama returned to Washington from a fundraising trip in California.

North Korea, incensed at fresh UN sanctions and US-South Korea military drills, has issued a series of apocalyptic threats of nuclear war in recent weeks.

Its armed forces said earlier they had received final approval for military action against the United States, possibly involving nuclear weapons.

While the barrage of threats from Pyongyang was familiar, Carney said it was nevertheless "obviously a concern," adding: "We're taking all the necessary precautions."

He reiterated that such "action and provocative rhetoric only serve to further isolate North Korea."