London: The US and South Korea warned North Korea of "further consequences" if it carried out a third nuclear test, as South Korea's outgoing leader suggested more than one test could be planned.
According to the BBC report, Lee Myung-bak, who leaves office later this month, told the Choson Ilbo that Pyongyang could be planning "multiple nuclear tests at two places or more".
North Korea said in January it was planning a "high-level nuclear test".
It has conducted two nuclear tests before, in 2006 and 2009.
Both followed the launch of long-range rockets, actions condemned by the UN as banned tests of missile technology.
Pyongyang has given no timeframe for the test, but analysts say satellite imagery indicates preparations at the test site in Punggye-ri are almost complete, with a tunnel in the mountainside apparently being sealed up, a key step before the test can take place.
On Sunday, North Korean leader Kim Jong-un issued what were described as "important" guidelines at high-level government meeting, another indication that the test is imminent.
The Washington-based Institute of Science and International Security has said that although recent satellite images "do not reveal whether a test is imminent, the on-going activity at the site justifies concern that a test will soon occur".
In a phone call on Monday, the new US Secretary of State John Kerry and his South Korean counterpart Kim Sung-hwan agreed that if North Korea "continues its provocative behaviour and takes further steps, that there must be further consequences", State Department spokeswoman Victoria Nuland told reporters.
The UN Security Council agreed in January to increase sanctions against North Korea after it carried out a long-range rocket launch in December. It also warned Pyongyang it would face "significant action" if the planned nuclear test went ahead.
But Mr Lee said it would be "difficult to persuade the North regime to give up the nuclear path", and that North Korea's reference to a "high-level" test could indicate it planned to detonate more than one device.
A test could also bring the country closer to miniaturisation of nuclear weapons, a key marker in turning nuclear devices into deployable weapons.
"If the North produces miniaturised weapons that can be used as warheads on missiles, it would really pose a threat," Mr Lee told the Chosun Ilbo newspaper. "That's why the whole world is watching it so intensively."
North Korea watchers have previously said that analysis of the test site indicates two tests could be being prepared.
The country's two previous tests have both involved plutonium devices, but some analysts say the threat of "high-level" testing could also indicate the North intends to detonate its first nuclear device made with highly-enriched uranium.
