The leaders of South Korea and the U.S. agreed Friday to reconsider the timing of Washington’s transfer of its wartime operational control of Korean troops, scheduled for 2015, in the face of persistent North Korean nuclear threats.

During their summit in Seoul, Presidents Park Geun-hye and Barack Obama also warned the communist state against conducting a fourth nuclear test, vowing further pressure and sanctions that have “even more bite.”

With Seoul-Tokyo ties remaining frosty, Obama took a swipe at Japanese leaders, urging them to “look back on the history” of Korean women who were forced to provide sex to Japanese troops during World War II.

The envisioned delay of the OPCON handover reflects the “evolving security landscape” in the region and will help ensure that the alliance is “fully prepared” against any eventualities, he said.

“The U.S. and South Korea stand shoulder to shoulder in the face of Pyongyang’s provocations and our refusal to accept a nuclear North Korea,” Obama told a joint news conference after their meeting at Cheong Wa Dae.

Concerns have been rising since the North threatened a fourth round of underground nuclear experiments late last month in protest against the U.N. Security Council’s condemnation of its test of midrange ballistic missiles.

Should the Kim Jong-un regime press ahead with what it said would be a “new form of nuclear test,” it will face a “new intensity of pressure,” Park said.

“We assess that North Korea has completed all necessary preparations for a fourth nuclear test and thus is ready to go ahead at any time,” she said.

“(The OPCON transition) should be implemented in a way that strengthens the South Korea-U.S. combined defense posture and has no negative impact on our security at all.”

Stressing Beijing’s role in inducing a change from its recalcitrant ally, the two presidents left the door open for Pyongyang yet reaffirmed that any talks should ensure substantive progress in its denuclearization.

North Korea’s atomic program poses a “direct threat” to not only its neighbors but also the U.S. itself, Obama said, calling the country “one of the principle proliferators of dangerous weapons around the world.”

“We don’t reward bad behavior. We don’t go through the constant cycle in which provocative actions by North Korea result in dialogue that leads nowhere,” he said.

“We’re not going to find a magic bullet that solves the problems overnight. The single most important thing is that we continue with the consistent, steady approach and strong unity of efforts … to prepare for eventualities while still opening the prospect for a negotiated resolution for this longstanding conflict.”

Touching on historical tensions between the U.S.’ top two regional allies, Obama pressed Japanese Prime Minister Shinzo Abe to stop denying and come clean about his country’s wartime atrocities.

Up to 200,000 women, mostly Korean, are believed to have been mobilized in frontline brothels during World War II. Of the 237 Korean women who came forward as former sex slaves, 55 are still alive.

Saying that what happened to the so-called comfort women was a “terrible, egregious and shocking” violation of human rights even in the midst of war, Obama called on both Seoul and Tokyo to “look forwards as well as backwards.”

The remarks marked a ratcheting-up of U.S. pressure compared with last February when U.S. Secretary of State John Kerry urged them to “put history behind them and move the relationship forward.”

Relations between the two Asian powers plunged to a new low after Abe visited the Yasukuni Shrine in late December, which venerates some 2.5 million Japanese war dead including top colonial leaders and war criminals responsible for massacres, sex slavery, forced labor and other cruelties.

Obama brokered a trilateral summit with Park and Abe in The Hague a month ago, facilitated by the nationalist premier’s pledge to uphold past administrations’ apologies. Yet his aides and other politicians continue revisionist remarks and behavior, enraging neighbors.

“(The former comfort women) deserve to be heard, they deserve to be respected. And there should be an accurate and clear account of what happened,” Obama added.

“I think Prime Minister Abe recognizes this and certainly the Japanese people recognize that the past is something that has to be recognized honestly and fairly.” 

Obama’s much-trumpeted visit was somewhat overshadowed by the sinking of a South Korean ferry that left more than 300 dead or missing, as well as the crisis in Ukraine.

As a token of condolence, he offered her a magnolia tree from the White House lawn and an American flag that was flying at the presidential grounds on the day of the disaster.

“So many were young students with their entire lives ahead of them,” said Obama, a father of two teenager daughters. Most of the victims are high school students. “I can only imagine what the parents are going through at this point, the incredible heartache.”

During their talks, Park and Obama also discussed ways to step up the implementation of the bilateral free trade pact and expand economic, cultural and people-to-people exchanges in line with their increasingly multifaceted alliance.

The U.S. president returned nine ancient Korean seals shipped out of the country at the height of the 1950-53 Korean War, which were seized from the family of a deceased veteran. Among them is the Hwangjejibo (Seal of the Emperor) made upon the 1897 foundation of the Korean Empire by King Gojong.

Shortly after his arrival, Obama visited the National War Memorial to lay a wreath in honor of the fallen soldiers of the Korean War and hold a celebration for 20 newly naturalized service members from 14 countries. He then continued to Gyeongbokgung Palace before heading to Cheong Wa Dae for the summit and dinner with Park.

Seoul is the second leg of Obama’s four-nation tour that will also take him to Malaysia and the Philippines. The two-day stay is his fourth as U.S. commander-in-chief.

On Saturday, he is scheduled to take part in a breakfast gathering with South Korean business leaders; visit the Combined Forces Command with Park, which is in charge of some 28,500 American troops stationed here; and give a speech at the Yongsan Garrison.

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