U.S. Secretary of State John Kerry gives a thumbs-up to the staff at Vatos Urban Tacos, during a stop at the restaurant in Seoul, Korea, May 18, 2015. (Pool/Reuters)

Secretary of State John F. Kerry on Monday accused North Korea’s government of committing crimes worthy of referral to the International Criminal Court and urged it to end its isolation by dismantling its arsenal of nuclear weapons.

Using strong language, Kerry said during a stop in Seoul that the Pyongyang government led by Kim Jong Un had shown a “flagrant disregard for international law while denying its people fundamental freedom and rights.”

“The world is hearing increasingly more and more stories of grotesque, grisly, horrendous public displays of executions on a whim and a fancy by the leader against people who were close to him and sometimes for the most flimsy of excuses,” he said, referring to a report from South Korea’s spy agency that the North Korean defense minister was publicly executed with an antiaircraft gun after he fell asleep during a meeting led by Kim.

Kerry vowed to speak out against “North Korea’s atrocities against its own people” and warned that Kim’s mercurial behavior is likely to lead other nations to push for charges against him and North Korea at the International Criminal Court in The Hague.

Kerry’s visit, planned weeks ago, comes in the wake of fresh concern about Pyongyang’s behavior.

Earlier this month, North Korea fired what it claimed was a ballistic missile from a submarine, although some analysts doubt that anything more lethal than a balloon was shot into the air.

Kerry’s Seoul stop was designed to underline the United States’ “ironclad” commitment to South Korea’s security and to ramp up pressure on Pyongyang to return to denuclearization talks it abandoned three years ago.

Since then, Kerry said, North Korea has rebuffed overtures from the United States, Russia, Japan and China to return to the negotiating table and instead is showing greater belligerence.

“They have grown the threat of their program and have acted with a kind of reckless abandon,” he said at a news conference alongside South Korean Foreign Minister Yun Byung-se.

Kerry said he hoped the negotiations to curb Iran’s nuclear program, now entering their final stretch, could serve as a model for North Korea to follow if the hermit kingdom wants to end its isolation.

“We are more determined than ever to find ways to convince Kim Jong Un and North Korea that all they are doing now is isolating themselves further and creating greater risks to the region and to their own country,” he said.

But he added a caveat: “We have to have some indication from the leader of North Korea that they’re serious about engaging on the subject of their nuclear program.”

At the news conference, Kerry also expressed gratitude to South Korea for the care and concern shown to U.S. Ambassador Mark Lippert recently after he was attacked in central Seoul by a suspected North Korea sympathizer and required hospitalization. Lippert, with bandages still on his cheek and left hand because of his injuries, accompanied Kerry to his meetings and joined him for lunch at a Seoul taco place run by Koreans who used to live in the United States.

“I want to take the opportunity to thank all the people of South Korea for the remarkable outpouring of concern about his health and their affection for him and for our country,” Kerry said.

He also said that the Islamic State militant group’s capture of the city of Ramadi in Iraq, although a setback, would prove temporary.

“Notice what they’ve done,” he said. “Huge numbers of vehicle-borne IEDs, big trucks, massive explosions. They’ve destroyed the place. That’s hardly a future. I’m convinced, as forces are redeployed and days flow in weeks ahead, that’s going to change.”

Kerry also touched on Yemen, where Saudi-led airstrikes against Shiite Houthi rebels resumed as a five-day cease-fire expired Sunday night. Kerry blamed the end of the truce on the rebels, saying that they had taken advantage of the pause in fighting to move missile launchers to the border with Saudi Arabia and that the Saudis acted to take them out.

“Under the rules of engagement, it was always understood if there were proactive moves by one side or another, it would be in violation of the cease-fire agreement,” he said. “Saudi Arabia, under the rules of engagement, took action to take out the missile launchers.”

In a speech later in the day at Korea University, an elite school with a cyber-law center, Kerry said everyone in the world should have the right to Internet access. He condemned repressive governments that silence critics by restricting Web access and singled out North Korea as the polar opposite of South Korea, one of the most wired countries on the planet.

“It is no coincidence many governments that have a poor record on Internet freedom also have a questionable commitment to human rights,” he said.

Read more:

Does North Korea execute people with antiaircraft guns? New satellite images suggest the rumors may be true.

North Korea releases list of U.S. ‘human rights abuses’: ‘The U.S. is a living hell’

South Korea should free conscientious objectors to military service, Amnesty says