There are fears North Korean dictator Kim Jong-un could launch a nuclear weapon as the global threat escalates.
The pariah state has finished preparations for its first nuclear test launch since 2017, according to South Korea's Foreign Minister Park Jin, who also called for a political resolution to bring it to a halt.
Meanwhile, US Secretary of State Antony Blinken has promised to "respond quickly" should the despot press the button and initiate his seventh test bomb.
Park said the North would pay the price for any displays of nuclear aggression, referring largely to sanctions against the self-isolated nation, and last week urged the tyrant to "make the right decision".
Park said: "If North Korea ventures into another nuclear test, I think it will only strengthen our deterrence and also international sanctions.
"North Korea should change its mind and make the right decision.”
Yesterday Blinken said Washington plans to maintain pressure on North Korea until Pyongyang changes course and de-escalates.
Park, his South Korean counterpart, urged China to persuade the North not to resume nuclear testing.
After the meeting, Blinken told reporters the US remains open to dialogue with Pyongyang but that calls had been ignored and missiles tested.
He added that preparations have also been made to resume nuclear testing for the first time since 2017.
"Until the regime in Pyongyang changes course, we will continue to keep the pressure on," Blinken told reporters, referring to U.S.-led international sanctions on North Korea.
Park said any provocations by North Korea, including a nuclear test, would be met with a united and firm response and urged China to use its influence.
Park said North Korea was at a crossroads - it could go ahead with a nuclear test and isolate itself, or return to diplomacy and dialogue.
"I also think China should play a very positive role to persuade North Korea that maintaining peace and stability on the Korean peninsula requires their new thinking," he said.
Park said he and Blinken had agreed on early reactivation of an extended deterrence working group, a policy body dealing with the U.S. nuclear umbrella that protects South Korea.
He said the body deals with deployment of strategic assets when necessary, but did not elaborate. Blinken said Washington was prepared to make short and longer-term adjustments to its military posture, as appropriate.
Blinken said he expected the working group would be back up and running in weeks ahead and said Washington and Seoul were committed to discussing how to expand the scope and scale of their combined military exercises.
Blinken said the United States had noted the appointment of North Korea's first female foreign minister last week, key nuclear negotiator Choe Son Hui, but added that the U.S. approach to a country was based its policies, not individuals.
Blinken also said Washington would continue to impose sanctions on Chinese and Russian individuals and entities aiding North Korea's missile and nuclear programs.
China's U.N. envoy told Reuters last week Beijing does not want to see another North Korean nuclear test, which is partly why it vetoed a U.S.-led bid to impose new U.N. sanctions on Pyongyang over renewed ballistic missiles launches.
But Ambassador Zhang Jun warned against making presumptions on how Beijing might react to a seventh test, which Washington has warned could happen at "any time."
In recent years China and Russia have been pushing for an easing of sanctions on North Korea on humanitarian grounds - and in the hope that it can be convinced to return to negotiations.
