The Navy's top officer in the Pacific has warned that the North Korea crisis is real – and the US must assume Kim Jong Un intends to launch nuclear attacks on America and its allies.

Admiral Harry B Harris Jr, Commander of US Pacific Command, said on Thursday that the crisis in the Korean Peninsula is the worst he'd since he began serving in 1978.

'There is some doubt within the intelligence community whether Kim Jong Un has that capability today or whether he will soon, but I have to assume he has it, the capability is real, and that he's moving towards it,' Harris said, according to Fox News.

'The North Korean crisis is the worst I've ever seen,' he said.

Harris was speaking to the Senate Armed Services Committee when he made the remarks.

He recognized that there were multiple possible threats in the Pacific theater – including the possibility of ISIS being pushed into the area from the Middle East.

But he said that North Korea remained the most urgent threat, as it is 'vigorously' pursuing the capacity to bomb the US, South Korea and Australia.