North Korea is warning it would take "merciless self-defensive" measures should the United States enforce a naval blockade, which Pyongyang sees as "an act of war", the isolated nation's state media reports.
Citing a foreign ministry spokesman, the North's KCNA news agency said on Thursday a naval blockade would be a "wanton violation" of the country's sovereignty and dignity.
US President Donald Trump was taking an "extremely dangerous and big step towards the nuclear war" by seeking such a blockade, it added. It was not immediately clear what US proposal the agency was referring to.
"Should the United States and its followers try to enforce the naval blockade against our country, we will see it as an act of war and respond with merciless self-defensive counter-measures as we have warned repeatedly," the agency said.
'Sleepwalking' into war
Chinese President Xi Jinping says war must not be allowed to break out on the Korean peninsula, while UN Secretary-General Antonio Guterres has warned of the danger of "sleepwalking" into conflict.
Mr Xi made his comments to visiting South Korean President Moon Jae-in just days after US Secretary of State Rex Tillerson offered to begin direct talks with North Korea without pre-conditions.
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But the White House said on Wednesday that no negotiations could be held until North Korea improved its behaviour. The White House has declined to say whether Mr Trump, who has taken a tougher rhetorical line toward North Korea, approved Mr Tillerson's overture.
North Korea tested its most advanced intercontinental ballistic missile on November 29, which it said could put all of the United States within range, in defiance of international pressure and UN sanctions.
The United States has said all options were on the table in dealing with North Korea, including military action.
While South Korea and China share the goal of getting North Korea to give up its nuclear weapons and stop testing increasingly sophisticated long-range missiles, the two have not seen eye-to-eye on how to achieve this.
Meeting in Beijing's Great Hall of the People, Mr Xi told Mr Moon that the goal of denuclearising the Korean peninsula must be stuck to, and war and chaos cannot be allowed, Chinese state media said.
"The peninsula issue must, in the end, be resolved via dialogue and consultation," Mr Xi was cited as saying.
Mr Guterres said Security Council resolutions on North Korea's nuclear and missile programs must be fully implemented by Pyongyang and other countries.
"Security Council resolutions must be fully implemented, first of all by North Korea, but by all other countries whose role is crucial," he said after meeting Japanese Prime Minister Shinzo Abe.
"The worst possible thing that could happen is for us all to sleepwalk into a war."