Kerry warning over nuclear test
North Korea will be punished if it carries out its threat to conduct a nuclear test, John Kerry has warned.
The new US Secretary of State John Kerry and his South Korean counterpart have discussed how to respond, amid signs that such a test is coming.
South Korea's president also speculated that Pyongyang may detonate multiple atomic devices simultaneously.
The UN Security Council passed a resolution last month condemning a North Korean long-range rocket launch that the UN and others call a disguised test of banned missile technology. It means Pyongyang is subject to new sanctions if it detonates its third nuclear device since 2006.
North Korea announced last month that it will conduct a nuclear test to protest against the toughened sanctions over its December launch, which delivered a satellite into orbit.
During a telephone conversation between Mr Kerry and South Korean Foreign Minister Kim Sung-hwan, "there was agreement that ... if the DPRK continues its provocative behaviour and takes further steps, that there must be further consequences," State Department spokeswoman Victoria Nuland said.
North Korea may simultaneously conduct multiple nuclear tests as it tries to create a warhead small enough to fit atop a long-range missile, South Korean President Lee Myung-bak has said.
A North Korean nuclear test "seems to be imminent," South Korea's UN Ambassador Kim Sook said at a news conference at UN headquarters in New York. He said there are "very busy activities" taking place at North Korea's nuclear test site "and everybody's watching".
The ambassador said he expects the Security Council to respond with "firm and strong measures" in the event of a nuclear test.
North Korea has denounced sanctions over its rocket launches, saying it has the sovereign right to use rockets to send satellites into orbit under a space development programme.