The US said it might "interdict" North Korea's maritime traffic.

Pyongyang called it a "big step" toward nuclear war.

North Korea consistently makes grand threats, but naval blockades have led to war in the past and would most likely require violence to enforce.



After North Korea's latest missile test late last month, US Secretary of State Rex Tillerson called on all nations to clamp down on the rogue nation and reasserted the US's "right to interdict maritime traffic" coming into and out of North Korea.

The threat riled Pyongyang, which has threatened war if its ships are blocked.

"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," North Korean media said, adding that it would be a "big step" toward nuclear war.

But North Korea consistently refers to the US's actions as "acts" or "declarations" of war, usually following with threats of war.

After North Korea's nuclear test in September, the US sought the UN Security Council's consent to interdict traffic, though that language wasn't included in the resolution it passed unanimously.

While North Korea's rhetoric tends to be vitriolic, naval blockades are typically considered an act of war because they usually require violence to enforce.

And there is precedent for such practices leading to war in the Pacific. In 1941, a US oil embargo on Japan was a prelude to the devastating attack on Pearl Harbor that dragged the US into World War II.