PHNOM PENH, Cambodia — Secretary of State Colin L. Powell sought Asian support yesterday for a new U.S. policy of interdicting suspect North Korean ships on the high seas, and North Korea threatened “immediate physical retaliation” if its vessels are stopped. “As you look at what happens on the high seas with respect to piracy, drug running, shipment of weapons of mass destruction, you can see that there could be a broader agenda for discussing maritime security,” Mr. Powell told reporters on his plane during the flight to Phnom Penh, where he is to attend a security meeting sponsored by the 10-nation Association of Southeast Asian Nations (ASEAN). “Whether these efforts will blend together at some point, it’s too early to say,” he added, referring to anything ASEAN members might do to help. The Bush administration reached an agreement last week with 11 allied countries to crack down on illicit North Korean trade. The communist nation has been caught shipping missiles to the Middle East and illegal drugs to Japan, Australia and other Asian nations. Mr. Powell said he would discuss the issue, known as the Proliferation Security Initiative with fellow foreign ministers today at the annual security meeting. “Everybody is saying the same things to the North Koreans with respect to the unacceptability of their actions,” Mr. Powell told reporters. The plan, also known as the Madrid Initiative for the city where last week’s meeting took place, was first proposed by President Bush during his European tour earlier this month. It was endorsed by Canada, France, Germany, Italy, Japan, Netherlands, Poland, Portugal, Spain and Australia. “Our goal is to work with other concerned states to develop new means to disrupt the proliferation trade at sea, in the air and on land,” John Bolton, undersecretary of state for arms control and international security who led the U.S. delegation in Madrid, told Congress on June 4. “Over time, we will extend this partnership as broadly as possible to keep the world’s most destructive weapons away from our shores and out of the hands of our enemies,” he said. North Korea’s official Rodong Sinmun daily called the measures part of a premeditated war plan yesterday. The North “will take an immediate physical retaliatory step against the U.S. once it judges that its sovereignty is infringed upon by Washington’s blockade operation,” the newspaper said in a commentary carried by the state-run KCNA news agency. “Nobody can vouch that this blockade operation will not lead to such a serious development as an all-out war.” The statement contained a warning to Japan, a major market for smuggled North Korean drugs. Tokyo has stepped up inspections of visiting North Korean ships on suspicion they are carrying drugs and intelligence agents. “In case a war breaks out on the Korean Peninsula, it will immediately spill over into Japan, as the territory of Japan is used as a U.S. base of aggression against [North Korea] and Japan is fully involved in the U.S. policy to isolate and stifle” North Korea, the paper said. Mr. Powell, who had a 15-minute impromptu meeting with North Korean Foreign Minister Paek Nam-sun at last year’s ASEAN meeting in Brunei, said yesterday that he is “pleased at the unity we have been able to achieve with the countries in the region” regarding the unacceptability of the North’s nuclear weapons program. It was not clear whether North Korea would attend this year’s meeting. Since their brief exchange nearly a year ago, the United States and North Korea have met twice: in Pyongyang in October, when the North admitted to having developed a secret uranium-enrichment program, and in April in Beijing, where the North Koreans told the U.S. delegation that they had nuclear weapons and intended to provide “proof” soon. “North Korea must understand that it does have to cease these activities and abandon altogether its nuclear programs,” said Australian Foreign Minister Alexander Downer, who is also in Cambodia for the ASEAN meeting, yesterday. U.S. officials said the initiative is a direct response to a December incident in which the United States and Spain seized a North Korean missile shipment for Yemen but had to let it go because no rules had been broken. Australia recently seized a North Korean boat loaded with amphetamines. Mr. Bolton warned that the administration’s goal is “not just to prevent the spread” of illicit arms, “but also to eliminate or roll back such weapons from rogue states and terrorist groups that already possess them or are close to doing so,” as it did in Iraq. Under the measure, Washington and its allies would be able to confiscate deliveries, preventing them from reaching their intended recipients. In the event that shipments are being transported by air, the plane carrying them would be denied overflight rights by countries that are part of the initiative, a State Department official said. The aircraft could also be grounded when stopping to refuel or even “escorted down” if they refuse to land, the official added. ASEAN includes Brunei, Burma, Cambodia, Indonesia, Laos, Malaysia, the Philippines, Singapore, Thailand and Vietnam. Each year, it invites other nations such as the United States to join security discussions as part of a group called the ASEAN Regional Forum.