SEOUL — Tensions on the Korean peninsula rose further Tuesday as Seoul announced that it would join a U.S.-led initiative to curb nuclear trade, and North Korea reportedly test-launched three more short-range missiles.
At the United Nations, representatives of the five permanent Security Council members, plus South Korea and Japan, began meetings that could lead to new sanctions against North Korea.
North Korea said Monday that it had conducted a nuclear test and several short-range missile launches, drawing sharp criticism from world capitals and a warning that it had violated a Security Council resolution.
A statement signed by ministers from more than 40 Asian and European countries urged the regime in Pyongyang to stop conducting nuclear tests and rejoin talks aimed at halting its nuclear program.
But South Korea's Yonhap news agency reported that North Korea had conducted three more missile tests, making a total of five this week. The news agency quoted South Korean officials as saying that two missiles were launched early in the day and a third Tuesday night.
And a South Korean newspaper reported today that U.S. spy satellites had detected steam from a nuclear reprocessing facility. Pyongyang had previously declared that it would restart reprocessing of fuel rods to harvest plutonium to protest criticism of a rocket launch in early April that was widely viewed as a test of missile technology.
South Korean officials said Tuesday that their country was joining 100 other nations in the so-called Proliferation Security Initiative, or PSI. North Korea has said it would consider participation by the South a declaration of war, and reiterated that today.
For months, South Korea had waffled on joining the largely symbolic naval blockade of ports that might trade in nuclear-related arms, concerned that the move would further alienate its neighbor.
In a statement, South Korean Foreign Ministry spokesman Moon Tae-young said the move came in response "to the grave threat to world peace and security from the proliferation of weapons of mass destruction and of missiles."
According to a U.S. intelligence report on the weapons trade, North Korea is one of the biggest exporters of ballistic missiles. It is also suspected of selling weapons of mass destruction and equipment used to develop missiles to countries in the Middle East and Southeast Asia, according to an unclassified report submitted to Congress.
In a telephone call to South Korean President Lee Myung-bak, President Obama praised South Korea for its support.
U.S. officials said Defense Secretary Robert M. Gates would meet with Japanese and South Korean defense ministers Saturday in Singapore to discuss the North Korean nuclear test.
Obama's national security advisor, Gen. James L. Jones Jr., said the administration was trying to verify whether North Korea had conducted more missile tests.
"But as much as the detonation itself, I think the fact that they have this kind of technology and are obviously willing to export it is very troubling," he said at a White House briefing.
In a statement, Pyongyang's state-run Korean Central News Agency accused Obama of "pursuing the same reckless policy as followed by the former Bush administration to stifle [North Korea] by force of arms."
It cited what it called the "dangerous scenario of the U.S. to put the Asia-Pacific region under its military control . . . as foolish an attempt as taking oil to extinguish a fire."
Pyongyang has long been opposed to the prospect of Seoul supporting the PSI, referring to President Lee as a traitor and his administration as "puppet authorities."
Lee Jong-joo, a spokeswoman for South Korea's Unification Ministry, said the proliferation initiative did not single out any country, but was meant as a blanket policy against nuclear proliferation.
"We have been telling the North that this is not a matter related to South-North Korea relations," she said. "I hope North Korea will not make any wrong perception on this level."
Officials in Seoul suggested that they would not actively harass North Korean vessels, while continuing to honor a 2005 maritime agreement with Pyongyang that stressed nonviolence.
Experts also questioned the effectiveness of Seoul's joining the PSI, saying the move could further complicate matters between the two Koreas.
"It's obviously [a move] that can escalate tensions," said Paik Hak-soon, director at the Center for North Korean Studies at Sejong Institute in suburban Seoul. "This is not an effective policy instrument to solve fundamental questions about denuclearizing North Korea."
Seoul also established new guidelines for South Koreans working in the jointly run Kaesong industrial complex, calling for them to avoid contact with workers from the North.
Ju-min Park of The Times' Seoul Bureau and Times staff writers Josh Meyer and Julian E. Barnes in Washington contributed to this report.