South Korea is in talks with the United States to deploy U.S. strategic assets on the Korean peninsula, a South Korean military official said on Thursday, a day after North Korea said it successfully tested a hydrogen nuclear device.
The underground explosion angered China, which was not given prior notice although it is North Korea's main ally, pointing to a strain in ties between the neighbours. The test also alarmed Japan and the White House said Prime Minister Shinzo Abe agreed with U.S. President Barack Obama in a telephone call that a firm global response was needed.
Obama also spoke to President Park Geun-hye of South Korea to discuss options.
A South Korean military official told Reuters the two countries had discussed the deployment of U.S. strategic assets on the divided Korean peninsula, but declined to give further details. After North Korea last tested a nuclear device, in 2013, Washington sent a pair of nuclear-capable B-2 stealth bombers on a sortie over South Korea in a show of force.
At the time, North Korea responded by threatening a nuclear strike on the United States.
South Korea, technically in a state of war against the North, said it was not considering a nuclear deterrent of its own, despite calls from ruling party leaders. The United States is highly unlikely to restore the tactical nuclear missiles it removed from South Korea in 1991, experts said.
The United States is also limited in its military response for fear of provoking an unpredictable regime in Pyongyang, said Anthony Cordesman, a defense policy expert at the Washington-based Center for Strategic and International Studies think tank.
"Any escalation in this region, any over-reaction can easily lead to not only a conflict between South and North Korea, but drag China and the United States and Japan into a confrontation," as well, Cordesman said.
Hours after the latest nuclear test on Wednesday, the U.N. Security Council said it would work immediately on significant new measures against North Korea. Diplomats said that could mean an expansion of sanctions against Pyongyang, although major powers might baulk at an all-out economic offensive.