South Korea vowed on Wednesday to take "stern" actions if North Korea launches a long-range missile or conducts another nuclear test.

The Unification Ministry said it is hard to predict whether the secretive North will go ahead with a rocket launch or a fourth nuclear test but stressed Seoul will respond resolutely to any provocation.

"North Korea's possible launch of a missile or conducting a nuke test are serious provocations and military threats. They are also a clear violation of the United Nations Security Council's resolutions," ministry spokesman Jeong Joon-hee told a regular press briefing.

"So if the North makes such provocations, Seoul will respond to them by collaborating with the international community in a proper and stern manner," he added.

On Tuesday, North Korea said it is fully ready to use nuclear weapons against the United States "at any time" and also announced that it has resumed the operation of its nuclear reactor at the Yongbyon complex.

Some analysts said the North strongly hinted at conducting a nuke test following its previous ones in 2006, 2009 and 2013, while others said that North Korea's threat is just saber rattling.

Late Monday, the North also vowed to launch what it called "a series of satellites" as it is preparing to mark the 70th anniversary of the founding of its ruling Workers' Party.

The North's threats are feared to cast a pall on South and North Korea's hard-won conciliatory mood on the Korean Peninsula following their landmark deal on Aug. 25 to defuse military tension.

Jeong said that there have been no detected signs for the North's possible missile launch or nuclear test so far.

"It is not proper for the government to prejudge the North signaling its fresh nuclear test," the spokesman said. "The government is concerned about such a possibility, but it plans to make any decision later after taking relevant issues into comprehensive consideration." (Yonhap)