朝鲜将进行第四次核试验
North Korea may be preparing for a fourth nuclear test, South Korean officials say.
韩国官员称，朝鲜可能正在准备进行第四次核试验。
South Korean Unification Minister Ryoo Kihl-jae told lawmakers there were signs of increased activity in the North's main nuclear test site.
North Korea has stepped up its habitual fiery（热烈的，暴躁的） rhetoric against the US and South Korea in recent weeks.
Correspondents say it is unclear whether a test is being prepared or it is a ruse to boost the sense of crisis.
Mr Ryoo did not elaborate on（详细说明） the specific intelligence which led South Korea to suspect the North was set to carry out its fourth nuclear test.
But when asked about a news report that North Korea had stepped up activity at the underground site it has used in previous tests, he said "there are such signs".
Kim Min-seok, a spokesman for South Korea's defence ministry, said it was possible that the North could fire a ballistic missile and conduct a nuclear test at the same time.
But the official Yonhap news agency quoted him as playing down the threat of an imminent（迫近的） test, saying there were several facilities at the nuclear test site so the movement of vehicles and people there was expected.
"Currently, there is no new movement to add on to the previous briefing," he said.
Newspaper JoongAng Ilbo quoted an unnamed South Korean official as saying that South Korean intelligence had detected "increased activity of labour forces and vehicles" at the Punggye-ri nuclear test site in the country's north-east.
"We are closely monitoring the ongoing situation, which is very similar to the situation ahead of the third nuclear test," the official told the newspaper.
"We are trying to figure out whether it is a genuine preparation for a nuclear test or just a ploy（策略，活动） to heap more pressure on us and the US."