SEOUL--Fresh off a stop in Tokyo, President Joe Biden’s top diplomat and defense chief traveled to South Korea on Wednesday, a day after North Korea made sure it had their attention by warning the United States to “refrain from causing a stink” amid deadlocked nuclear negotiations.

How to get North Korea to return to talks will be a major focus when Secretary of State Anthony Blinken and Defense Secretary Lloyd Austin meet South Korean officials this week.

It has been more than two years since nuclear talks stalled, and some experts say the United States and its allies should settle for a deal that would freeze North Korea’s nuclear program in return for relaxing sanctions--and possibly leave Pyongyang’s already manufactured nuclear weapons in place.

Austin and Blinken will meet their South Korean counterparts for separate talks Wednesday and a joint “two plus two” meeting Thursday, the first such contact between the two countries in five years.

South Korea is the second leg of their regional tour aimed at boosting America’s Asian alliances to better deal with growing challenges from China and North Korea. While in Tokyo on Tuesday, they joined forces with Japanese officials to criticize China’s “coercion and aggression” and reaffirm their commitment to ridding North Korea of all its nuclear bombs.

U.S.-led diplomacy on that last topic has been in limbo since a February 2019 summit between President Donald Trump and North Korean leader Kim Jong Un collapsed over disputes on U.S.-led sanctions. Kim has since threatened to enlarge his nuclear arsenal in protest of what he called U.S. hostility.

On Tuesday, Kim’s sister and a senior official in her own right, Kim Yo Jong, slammed the United States over its ongoing regular military drills with South Korea, which North Korea sees as an invasion rehearsal.

“We take this opportunity to warn the new U.S. administration,” Kim Yo Jong said in a statement. “If it wants to sleep in peace for (the) coming four years, it had better refrain from causing a stink at its first step.”

Some experts say Kim Yo Jong’s statement is a pressure tactic and that Pyongyang may try to further raise animosities with weapons tests to boost its leverage in future negotiations with Washington.

Asked about Kim Yo Jong’s statement during a news conference in Tokyo, Blinken said that he was familiar with the comments and was more interested in hearing from allies and partners.

Blinken said that Washington reached out to North Korea through several channels starting in mid-February, but it hasn’t received any response. He said the Biden administration is looking forward to completing its policy review on North Korea in coming weeks and was looking both at possible “additional pressure measures” and “diplomatic paths.”

Shim Beomchul, an analyst with the Seoul-based Korea Research Institute for National Strategy, said he expects the Biden administration to pursue a deal with North Korea that resembles a 2015 accord that froze Iran’s nuclear program in return for lifting sanctions. While the United States won’t likely give up its long-term commitment to denuclearizing North Korea, rolling back the country’s nuclear capabilities to zero is not a realistic near-term diplomatic goal, he said.

Trump blew up that 2015 Obama administration deal in favor of what he called maximum pressure against Iran, and the Biden government is trying to resurrect it.

In an op-ed in the New York Times in 2018, Blinken, then a managing director of the Penn Biden Center for Diplomacy and Global Engagement, argued that the best deal the U.S. could reach with North Korea “more than likely will look like what Barack Obama achieved with Iran.” He said that an interim agreement “would buy time to negotiate a more comprehensive deal, including a minutely sequenced road map that will require sustained diplomacy. That’s the approach Mr. Obama took with Iran.”

Other experts say an Iran-style deal won’t work for North Korea. Iran hasn’t built any bomb, but North Korea has already manufactured dozens. They say North Korea, which has a history of derailing agreements with its vehement rejection of verification processes, won’t find any reason to denuclearize when some of the most painful sanctions are lifted.

“Everyone can say easily that (settling for) a nuclear freeze would allow North Korea to preserve its existing nukes. But I ask them what other options do they have” to realize North Korea’s denuclearization, said Kim Yeol Soo, an analyst with South Korea’s Korea Institute for Military Affairs.

Another possible topic during U.S.-South Korean talks is whether South Korea should actively participate in U.S.-led efforts to curb China’s rising strength in the region.

South Korea is a longtime U.S. ally and hosts about 28,500 American troops. But its economy is heavily dependent on trade with China, making it difficult to take any step deemed provocative to its biggest trading partner. When South Korea allowed the United States to install anti-North Korea missile defense shield on its soil in 2017, it suffered economic retaliation from China, which sees the system’s radar as a security threat.

South Korean Defense Minister Suh Wook told lawmakers Tuesday that the U.S. hadn’t formally proposed for South Korea to join an expanded format of the so-called “Quad” group that includes the United States, Japan, Australia and India, and that the Americans won’t likely make such a proposal during this week’s talks.

China has called the Quad an attempt to contain its ambitions.

Kim Yeol Soo said the allies will likely discuss Seoul joining an expanded Quad format, known as the Quad Plus, though they’ll never publicly announce it to avoid angering China. Kim said it would be “wise” for South Korea to join the Quad Plus to voice its opinions clearly and avoid being sidelined on issues involving Seoul.