His visit came one day after President Park Geun-hye and Unification Minister Rhyu Kihl-jae offered dialogue to the communist regime to settle the disputes over the recently suspended joint industrial park in the border city of Gaeseong.

The North blocked the entry of South Korean workers and cargo starting April 4 and pulled out all its 53,000 workers from the complex five days later.

The shift in the mood in Seoul coincided with U.S. gestures to curb pressure on the North.

Kerry said Obama had instructed to postpone a planned test launch of an intercontinental ballistic missile. That followed a series of Washington’s shows of force involving stealth and nuclear bombers, cutting-edge fighters and an atomic submarine during its joint military drills with the South.

"I think we have lowered our rhetoric significantly and we are attempting to find a way for reasonableness to prevail here,” he said.

The former longtime senator with diplomatic expertise expressed confidence in Park’s “trustpolitik” vision on which he was briefed during their meeting earlier in the day.

“President Park was elected with a different vision for the possibilities of peace and we honor that vision,“ Kerry said, adding that her first summit with U.S. President Barack Obama will be “productive, positive and constructive when it takes place on May 6.”

During a meeting at Cheong Wa Dae, Park told Kerry that the trust-building process for the Korean Peninsula was on-going and that while any provocation by Pyongyang would be sternly dealt with, she was working to allow common development of the two Koreas to be accomplished by accumulating trust if the North accepts change and comes to dialogue, the presidential office said in a statement.

Kerry in response praised the approach that he expected would draw a line against the North’s pattern in the past. He also affirmed the U.S. government’s commitment to strongly deal with any threat or provocation by the North.

The two talked for over an hour, well past the scheduled time, to discuss North Korea, Seoul and Washington’s alliance, nuclear energy cooperation negotiations, Park’s visit to Washington next month, and other regional matters.

Kerry said he will raise the issue with Chinese leaders when he touches down in Beijing on Saturday because they have “enormous ability” to help rein in the bellicose leadership in Pyongyang.

“I think it’s clear to everybody in the world that no country in the world has a closer relationship with and (more of a) significant impact on (North Korea) than China,” Kerry said.

But he said that a peaceful Korea must be free of atomic weapons, reiterating Washington’s pledge to defend its allies.

“North Korea will not be accepted as a nuclear power. The rhetoric that we are hearing from North Korea is simply unacceptable on any standard,” Kerry said.

He arrived here as part of his 10-day tour to Europe, the Middle East and East Asia, following Yun’s trip to Washington last week.

Obama also on Thursday urged Pyongyang to “end the belligerent approach they have taken and to try to lower temperatures.”

During his meeting with U.N. Secretary-General Ban Ki-moon, Obama reiterated his pledge to “take all necessary steps” in case of a North Korean provocation.

“Nobody wants to see a conflict on the Korean Peninsula,” he added.

North Korea, for its part, appears to be toning down its hostile rhetoric against the allies, following weeks of brazen threats.

It has been preparing and begun taking in foreign visitors for the celebrations of the birth of its late founder, Kim Il-sung, official media said.

The North is technically ready to fire its Musudan mid-range missile which has recently been moved to its east coast, according to South Korean and U.S. officials.

A U.S. intelligence report unveiled Thursday concluded that the regime has achieved the knowhow to arm a ballistic missile with an atomic warhead, though it said the weapon was unreliable.

Yun said South Korea and the U.S. would start a new round of negotiations in the near future on a bilateral civilian nuclear energy pact, which Seoul seeks to revise to be able to reprocess spent fuel.

The upcoming talks would be the first since February 2012. In August 2010, the allies first began official negotiations over the 1974 pact, which expires in March 2014.

Seoul has also stressed the need for the revision as tons of nuclear waste has been piling up with storage space running short. Storage capacity for the Kori nuclear power plant is expected to reach its saturation point in 2016.

But Washington has expressed concerns that any amendment could hurt its global non-proliferation efforts given that the reprocessing process could lead to the production of weapons-grade fissile materials.

Observers have said the timing was not favorable for Seoul as U.S. public sentiment has worsened against proliferation issues due to prolonged nuclear standoffs with Pyongyang and Tehran. 

By Shin Hyon-hee (heeshin@heraldcorp.com)