South Korea warned that a further escalation of tensions would disrupt joint economic projects that could bring badly needed investment to the communist North.
Citing safety concerns, Japan barred a North Korean ship from entering port amid a crackdown on alleged drugs and weapons smuggling by the North that has already led to six vessels being searched and one of those detained.
Meanwhile, U.S., Japanese and South Korean envoys were meeting in Honolulu to discuss the situation in North Korea.
Separately, Washington's top missile commander is in Tokyo for talks on a joint missile shield to protect Japan from any potential attack by the North.
The warnings and meetings indicate a toughening of the stance toward North Korea in by the United States, Japan, South Korea and Australia, which have been increasing pressure on the North to abandon its suspected development of nuclear weapons.
In recent months, North Korea has acknowledged possessing nuclear weapons both publicly and in discussions with Western envoys. Some observers wonder if that's true, or a pressure tactic to win more aid.
In an interview, Secretary of State Colin Powell says he takes North Korea at its word that it has developed nuclear weapons but "we will not be frightened into taking action that would not be appropriate."
The Bush administration seeks a diplomatic solution "and we feel confident that one can be found."
In recent weeks, Japan and Australia have tightened inspections on North Korean ships suspected of smuggling narcotics, counterfeit money and missile technology — believed to be the regime's three main sources of hard currency.
Japan has beefed up inspections of North Korean ships after a North Korean defector testified before U.S. Congress last month that a North Korean ferry was used to smuggle missile parts to the isolated country.
Since then, Japan has inspected six of the nation's ships for immigration, customs, health and safety violations — threatening to detain those with problems.
It is part of a joint pledge by Prime Minister Junichiro Koizumi and President Bush to stem the flow of illicit money and weapons they say underpins the Pyongyang regime and its ambition to build nuclear weapons.
North Korea denies involvement in smuggling.
"We've never conducted any illegal trade. All our past shipments were legal," said Han Jong Chi, director of the international affairs bureau of the General Association of Korean Residents in Japan, North Korea's de facto representative here.
North Korea on Friday urged South Korea to work with Pyongyang for the peaceful reunification of the divided peninsula without "relying on outsiders."
South Korean Unification Minister Jeong Se-hyun said South Korea was willing to push ahead with political reconciliation and economic cooperation with North Korea, as agreed upon in an unprecedented inter-Korean summit three years ago Sunday. But he added that nuclear tensions should ease before such projects can gain speed.
South Korea has been pursuing a policy of reconciliation with North Korea since their summit. But that policy has been challenged since U.S. officials announced last October that North Korea had admitted running a secret nuclear program in violation of a 1994 agreement.
On June 19, the two Koreas are scheduled to begin a new round of temporary reunions of Koreans separated by the war.
Last month, South Korea agreed to provide North Korea with 400,000 tons of rice this year to help ease chronic food shortages that have killed hundreds of thousands of people. But it later said it would delay shipments if North Korea escalates tensions.
In other developments: