President Park Geun-hye on Wednesday asked Chinese President Xi Jinping to persuade North Korea not to conduct a nuclear test amid growing concerns that Pyongyang may push ahead with a fourth atomic test ahead of US President Barack Obama's visit to Asia.
During a phone call between the two leaders, Park made the request and stressed that another nuclear test by the North would change the security landscape in Northeast Asia, her office said.
"President Park told Xi that an additional nuclear test by North Korea could spark an arms race and a nuclear domino effect that could fundamentally change the security landscape in Northeast Asia, and make all efforts to resume the six-party talks in vain," said presidential spokesman Min Kyung-wook.
In return, Xi told Park that China also hopes to ease tension on the Korean Peninsula and that the country has also made efforts to help maintain peace and stability in the region, Min said.
Xi also pointed out that China, like South Korea, opposes the North's nuclear programs.
Concerns have been growing since Pyongyang threatened a "new form of nuclear test" late last month in protest against the UN Security Council's condemnation of its test-firing of ballistic missiles.
Though no signs were spotted of an impending underground explosion, Seoul officials said they were detecting lots of activity at North Korea's nuclear site in the northeastern town of Punggye.
The South Korean military is believed to have observed an increase in vehicle and personnel movement there, as well as a screen to cover a tunnel.
Maintaining its security level at high, Seoul's Defence Ministry said on Wednesday that North Korea has completed its preparations to carry out its nuclear protest.
"North Korea is technically ready to conduct a nuclear test at any time," an official who declined to be named.
"It is like having an open plane ticket. (The North) is ready to take the plane at any time."
The comment came after the US think tank at Johns Hopkins University posted a conflicting analysis on Tuesday that North Korea is unlikely to be ready to stage the nuclear test during Obama's Asia tour.
"That may be possible but appears unlikely based on the limited commercial satellite imagery available and observations of past North Korean nuclear tests," 38 North said in a report. "Recent operations at Punggye-ri have not reached the high level of intensity ― in terms of vehicle, personnel and equipment movement ― that occurred in the weeks prior to past detonations."
The United States said Tuesday it was also watching the North "very closely."
"North Korea has a history of taking provocative action and we are always mindful of the possibility that such an action could be taken," White House spokesman Jay Carney told reporters aboard Air Force One as Obama departed for his weeklong trip to Asia. Obama arrives in Seoul on Friday for a two-day stay.
Carney said any action taken by North Korea would "most likely be in violation of numerous commitments that the DPRK (North Korea) is bound by, but of course that is something that they unfortunately have done many times."
He declined to comment on the validity of a South Korean Defence Ministry briefing that cited increased activity at North Korea's main nuclear test site. "We'll be watching it very closely," Carney said.
Meanwhile, Pyongyang vowed not to dump its nuclear weapons, against Seoul's demands.
South Korea "should not even dream that we will be coaxed into laying down our nuclear" programs by sweet talk, the North's Committee for the Peaceful Reunification of Korea said in comments carried by the country's official Korean Central News Agency.