N Korea mad about Kim Jong-un 'crazy fat kid' comment

North Korea is seeing red after US Senator John McCain called Kim Jong-un a "crazy fat kid".

Mr McCain, Armed Services Senate Committee chairman, made the comment on MSNBC last week, prompting a fiery response from Pyongyang, which called it "tantamount to a declaration of war".

Mr McCain's comments were in relation to increasingly erratic behaviour by the isolated country, including recent missile tests.

"The point is China is the only one that can control Kim Jong-un, this crazy fat kid that's running North Korea," the former Republican Presidential candidate said.

"The Chinese have to understand that there's a penalty that'll be imposed by us if they don't reign in an individual that literally could start a world war and in the short-term strike the United States of America."

In response, the North Korean government-controlled news agency KCNA released a highly critical statement, saying the comments "hurt the dignity of the supreme leader of the DPRK".

"[It is] just a manifestation of their worst hostility toward the DPRK's ideology and social system and its people and a grave provocation little short of declaration of war against it," the statement reads.

The response also singled out Republican Senator Ted Cruz, who earlier this month introduced legislation which would put North Korea back on a list of state sponsors of terrorism.

"They will have to bitterly experience the disastrous consequences to be entailed by their reckless tongue-lashing and then any regret for it will come too late," the government said, while delivering its own tongue-lashing.

But Mr McCain hasn't backed down from his comments, tweeting: "What, did they want me to call him a crazy skinny kid?"