The United States on Monday warned the Democratic People's Republic of Korea (DPRK) not to undertake another nuclear test or missile launch.

"Any future nuclear test or missile launch would be in direct violation of UN Security Council resolutions, and would lead to further pressure and isolation," State Department spokesman Patrick Ventrell said at a regular news briefing.

"So, we would strongly discourage against that course of action," he added, refusing to say what actions might be taken by Washington in the event of a fresh nuke test or missile launch by the DPRK.

Earlier in the day, South Korea's Unification Minister Ryoo Kihl-jae told lawmakers that there were signs that the DPRK was preparing for its fourth nuke test. Later, the country's Defense Ministry denied such a saying.

Tensions have been running high on that peninsula since the DPRK conducted its third nuclear test on Feb. 12 in protest against joint military drills conducted by Seoul and Washington.

The DPRK has even declared "a state of war" with the South and threatened to launch a preemptive nuclear strike for self-defense, naming military bases in the U.S. territory of Guam and the U.S. state of Hawaii as possible targets.