The warning came as the United States, Japan and Australia, began cracking down on the North Korean trade in illicit drugs, weapons and counterfeit money — believed to be key sources of hard currency for Pyongyang to buttress its regime and its suspected nuclear weapons programs.
North Korea's main state-run newspaper Rodong Sinmun claimed Tuesday that the United States is "laying an international siege to the North and putting a blockade against it as a premeditated scheme to start a new war on the Korean peninsula."
North Korea will take "physical retaliation," including "all means and methods an independent country can take," if it concludes that the recent moves by the allies violate its sovereignty, Rodong said in a commentary carried by the North's official news agency KCNA.
"There is no guarantee that this blockade will not lead to such a serious condition as a full-scale war," said Rodong. "If war breaks out between the North and the United States, it will not be limited to the Korean Peninsula but all the areas where aggressors are lurking will become our targets."
North Korea accused Japan of turning itself into the "base camp for U.S. aggression against Korea."
North Korea traditionally churns out saber-rattling rhetoric when its relations with the outside world worsen. Earlier this year, it warned that any new sanctions imposed on it would be treated as acts of war.
In Phnom Penh, Cambodia, the fight against terrorism and North Korea's nuclear program were expected to top the agenda at a meeting of Southeast Asian nations.
A draft statement by the forum of more than 20 Asian-Pacific countries called for a "peaceful solution of the nuclear problem" on the Korean Peninsula "for the sake of durable peace and security in the region."
Japan has been tightening safety and customs inspections of North Korean ships long suspected of smuggling missile parts and narcotics between the two countries. In the past week, they have detained one cargo ship and blocked another from docking for safety violations.
The move came after a North Korean defector told U.S. lawmakers last month that a North Korean ferry linking the two countries was used to smuggle missile parts.
Japan allows trade with North Korea on an informal basis, though the two countries have no diplomatic relations. Last year, 147 North Korean ships made over 1,300 port calls in Japan.
In a joint statement in Hawaii last week, U.S., Japanese and South Korean officials expressed concern about the North's narcotics trafficking and counterfeiting, and said they discussed cooperation to stop them.
In the past few days, both Japanese and South Korean officials have said that intensifying pressure on North Korea would force it to accept a U.S. offer for multilateral talks on halting its suspected nuclear weapons programs.
In April, Australian authorities raided a North Korean-owned ship and charged its crew with aiding and abetting the trafficking of heroin.
Tensions in the region have been mounting since October, when U.S. officials said North Korea admitted having a covert nuclear program. The United States and its allies cut off free oil shipments. North Korea retaliated by quitting the Nuclear Non-Proliferation Treaty and restarting its nuclear facilities.
North Korea has since announced publicly that it is seeking nuclear weapons and told American envoys that it already has "the bomb" and plans to reprocess fuel rods to create material that could be used to make more.
Pyongyang claims nuclear weapons are necessary both to counter the new, U.S. policy of preemptive strikes and to allow the cash-strapped North to whittle down its massive, costly conventional force.
Some observers believe the North, which has suffered from years of crop failures and receives billions in food assistance, is pressing for more aid.