South Korea's unification minister has warned that North Korea's proposed third round of nuclear testing will be a major threat to the region.
Yu Woo-ik and Kim Sung-hwan, foreign minister, attended a foreign affairs, unification and trade committee meeting on Monday to answer politicians' questions on North Korea's atomic tests.
Yu said that North Korea was likely to carry out another nuclear test, but did not elaborate on a detailed time-frame.
"If the final step of the nuclear test is successfully executed, it is to be pointed out that the security of the Korean peninsula will work on different factors," he said.
The South Korean defence ministry also voiced concern on Monday, warning North Korea not to further provoke South Korea.
"If the North Korea nuclear test takes place, it is a provocation against the international community. This is a major provocation against South Korea," Kim Min-seok, defence ministry spokesman, said at a briefing session.
There has been a boost in diplomatic activity in the region following the North's announcement last month that it will conduct the nuclear test to protest international sanctions toughened over Pyongyang's long-range rocket launch in December.
Show of force
Yu's statement came as South Korean and US troops began naval drills on Monday in a show of force partly directed at North Korea.
Three-day exercises began off the Korean Peninsula's east coast that involve live-fire exercises, naval manoeuvres and submarine detection drills.
Al Jazeera's Harry Fawcett, reporting from Seoul, said the timing of the so-called combat-readiness tests by South Korea and the US was significant.
"They are excercises of a very large in scale in terms of two large US ships, a submarine and an Aegis equipped cruiser - that is, the anti-missile defence and shooting down system the US has," he said.
"There is also an Aegis-equipped South Korean vessel, as well as nine other South Korean vessels. So these things take a good amount of time to plan.
"They could not have been put together in the last few days, in terms of responding to North Korea's nuclear test.
"But certainly the timing is significant and a senior South Korean military official did allow himself to be quoted here, saying it is a show of force to Pyonyang at this time."
North Korea's two previous nuclear tests, in 2006 and 2009, both occurred after it was slapped with increased sanctions for similar rocket launches.
The US, South Korea and other countries have urged North Korea to end its nuclear test plans or face serious consequences.
North Korea's state media said on Sunday that at a high-level Workers' Party meeting, leader Kim Jong-un issued "important" guidelines meant to bolster the army and protect national sovereignty.
North Korea also says it has the sovereign right to launch rockets to send satellites into orbit under a space development programme.
The US says the December launch was a disguised test of banned missile technology.