North Korea has warned the US would take a "dangerous and big step" towards nuclear war if it enforces a naval blockade.
It said it would take "merciless self-defensive" measures.
North Korea state media said the Trump administration was "pursuing a policy of military confrontation but this is nothing but a death-bed struggle by those alarmed by the might of the DPRK always emerging victorious".
"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," said KCNA, citing a foreign ministry spokesman.
Although a blockade to enforce trade sanctions is not believed to be imminent, after North Korea's November rocket test US Secretary of State Rex Tillerson said it was a possibility.
White House National Security adviser HR McMaster said in September however, that even 'non-strike' options carried the risk of military escalation.
North Korea's latest threat comes as Chinese President Xi Jinping - during a visit by South Korea's leader - said war must not be allowed to break out.
"The peninsula issue must, in the end, be resolved via dialogue and consultation," he said.
South Korea's Yonhap news agency said the presidents had agreed to cooperate in applying sanctions and pressure on the North.
UN chief Antonio Guterres also said on Thursday that it was vital Security Council resolutions on North Korea were fully implemented by all countries.
"The worst possible thing that could happen is for us all to sleepwalk into a war," Mr Guterres said during a visit to Tokyo to meet Japan's PM.
North Korea's leader Kim Jong Un continues to defy the international community with regular missile tests and threats of nuclear strikes against the US mainland if provoked.
The latest test - of a long-range Hwasong-15 rocket - was last month.
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Despite President Trump's bombastic language and counter-threats, Mr Tillerson recently offered direct talks with North Korea without pre-conditions.
Russia's Vladimir Putin - speaking at his annual news conference on Thursday - said a pre-emptive US strike against North Korea would be "catastrophic" and called Mr Tillerson's offer a "realistic" approach.
The UK maintains that economic pressure is the best way to deal with North Korea.
Speaking at a news conference, Foreign Secretary Boris Johnson said: "We don't want to see a military solution... we want to see an intensified diplomatic effort."