North Korea called the meeting with U.S. Secretary of State Mike Pompeo “regrettable” which contrasted with the statement from the former C.I.A. boss that the talks were very productive.

On Friday, Pompeo arrived in Pyongyang, the capital of North Korea, to meet with Kim Yong Chol, the senior aide to the communist state’s leader Kim Jong-Un.  Chol played an important role in the previous summit in Singapore on June 12 between President Donald Trump and Jong-Un. Pompeo did not meet with Jong-Un during his third visit to North Korea.

“We had expected that the U.S. side would offer constructive measures that would help build trust based on the spirit of the leaders’ summit. We were also thinking about providing reciprocal measures,” said a spokesperson from the North Korean foreign ministry whose name was not identified in a statement published by the official Korean Central News Agency.

“However, the attitude and stance the United States showed in the first high-level meeting [between the countries] was no doubt regrettable,” the spokesperson continued.

While Pompeo described the meeting as “positive” and “productive,” Pyongyang accused the U.S. of trying to pressure North Korea to meet Washington’s denuclearization demands.

“The North Koreans have also confirmed the missile engine testing facility, we talked about how the modalities will look like for the destruction of this facility. There is progress [on the issue],” Pompeo briefed the press.

The statement came shortly after Pompeo claimed he had made progress in his meeting with the North Korean side. He said both sides had agreed to meet on July 12, in Panmunjom to discuss the returning of remains of American soldiers killed in the Korean War.

Washington and Pyongyang still differ on the definition of denuclearization

On June 12, President Trump and Jong-Un met in a historic summit in Singapore. At that time, both leaders loosely agreed to dismantle nuclear weapons and make peace in the Korean Peninsula.

While both leaders professed a commitment to peace, the agreement was short on details on how denuclearization would be achieved or even what was meant by “denuclearization.” Both countries have historically had different interpretations of denuclearization.

North Korea has claimed it’s willing to abandon its nuclear weapons if the U.S. withdraws its troops from South Korea and ends its military alliance with Seoul. North Korea also wants a guarantee that the U.S. removes economic sanctions. While Washington wants a more sweeping implementation of denuclearization that would phase out the entire nuclear threat imposed by North Korea and give up their supply of nuclear weapons under irreversible and verifiable manners. The U.S. also wants to halt Pyongyang’s ability to enrich and produce ingredients of nuclear power, namely uranium and plutonium.

Last April, Jong-Un announced North Korea would discontinue its nuclear activities, stating that the world had already recognized the country’s nuclear ability.

How long will denuclearization take?

Many North Korea experts have previously warned that dismantling North Korea’s nuclear weapons is not an easy task, despite Trump’s demand for quick denuclearization.

According to a report from Stanford University, it may take a decade or more for North Korea to denuclearize, given its material stockpile recorded as of the end of 2017.

Siegfried Hecker, the nuclear expert at Stanford University, has visited North Korea seven times. He estimated that North Korea could produce around 20 to 40 kilograms of plutonium, it may take five or six kilograms to make a bomb.

“Could they have an overall bomb program that’s ten times as large? No. Could they have one that’s twice as large as what we think? The answer is possibly,” said Hecker.

Lindsey Ford, a former Asia policy adviser at the Pentagon, expressed the challenges to denuclearizing the Korean peninsula by comparing it to the difficulties the U.S. had with achieving an agreement with Iran. She noted that, unlike North Korea, Iran did not even have nuclear weapons.

“If you look back at the nuclear negotiations that we had with Iran and how long that took and how many times that almost fell apart, it gives you a sense of the degree of difficulty actually trying to roll back a nuclear program,” Ford said.