This week's announcement of a nuclear test by North Korea has sent seismic tremors through South Korean politics. The South's government says it may join a U.S.-led effort to keep the North from exporting nuclear materials. But critics say the idea is far too risky.
The Proliferation Security Initiative, or PSI, is a United States-led international coalition dedicated to preventing the spread of weapons of mass destruction.
South Korea has previously kept its distance from the initiative, largely because of its sensitive relationship with North Korea, which is suspected of trading in missiles and other weapons.
However, now that Pyongyang has said it has tested a nuclear explosive, the South Korean government wants to participate.
Vice Foreign Minister Yu Myoung-hwan told lawmakers this week that South Korea plans to participate in PSI on a partial and case-by-case basis.
The initiative includes stopping and searching ships that are suspected of carrying weapons material.
Kim Geun-tae, chairman of South Korean President Roh Moo-hyun's Uri party, argued passionately Thursday against taking part in such activities.
Kim warns increasing South Korea's participation in PSI could spark an armed conflict between the Koreas.
Japanese Defense Agency Chief Fumio Kyuma expressed similar concerns Thursday, in a session with his country's lawmakers.
He says it is difficult to know how North Korea would react to interdiction of its cargo ships. He warned that a hostile response could threaten Japan's peace and security.
Some South Korean leaders argue Seoul should not make a decision on PSI until it sees the final version of the United Nations Security Council resolution in response to North Korea's test.
The United States is expected to propose a resolution that imposes a strict arms embargo, financial sanctions and a ban on imports of luxury goods.
South Korea's parliament passed a resolution Thursday condemning the North's test announcement on Monday.
Kim Hyong-oh, a senior member of South Korea's main opposition party, says Seoul should back the PSI as soon as possible.
Kim says it is impossible to combine pressure and dialogue, and that South Korea needs to choose one or the other. Under the circumstances, he says, Seoul should choose to pressure the North.
Kim and other opposition leaders say President Roh's policy of engaging the North has been too lenient. Mr. Roh said this week that policy would need to change.
Alexander Vershbow, the U.S. ambassador to South Korea, earlier this week said Washington approves of Seoul taking a more active role in containing the North's activities.
"I hope the South Korean government increases its participation in the PSI after the North's nuclear test," he said.
North Korea has warned it would view international sanctions as a declaration of war.