North Korea vowed today to meet any US-led blockade with "limitless" retaliation.
The Marxist state is facing deepening international ostracism and mounting pressure from the United States and its allies over its pursuit of nuclear weapons.
The nuclear crisis has also thrown a spotlight on North Korea's alleged trade in arms and illegal drugs, prompting plans by the United States and its allies to curb such traffic. North Korea has rejected the allegations as groundless.
US and South Korean officials say any policing action would merely enforce existing laws and not represent sanctions or a blockade.
But a quarantine would not work without the help of China and Russia, which share borders with North Korea, experts say.
North Korea's official Rodong Sinmundaily said the moves were part of a premeditated war plan.
"[North Korea] will take an immediate physical retaliatory step against the US once it judges that its sovereignty is infringed upon by Washington's blockade operation," said the newspaper. "Nobody can vouch that this blockade operation will not lead to such a serious development as an all-out war".
In a meeting with South Korea and Japan in Hawaii at the weekend, the United States won support for efforts to clamp down on North Korean contraband.
Eleven countries, including the United States, agreed to join forces to find a way to block North Korean ships suspected of carrying drugs, counterfeit money or materials for weapons of mass destruction.