U.S. President Donald Trump hailed “big progress” as North Korean leader Kim Jong Un pledged to halt nuclear testing, a largely symbolic gesture that appeared aimed at softening the ground for talks between the two leaders.

Kim told a ruling party meeting in Pyongyang on Friday his regime would suspend tests of atomic bombs and intercontinental ballistic missiles after achieving its goal of building a nuclear arsenal, the official Korean Central News Agency reported. North Korea will shutter its Punggye-ri test site, a secluded mountain facility believed to be damaged after a hydrogen bomb test in September.

While the moves mostly affirm the status quo — North Korea hasn’t conducted a major weapons test in almost five months — Kim’s remarks to a domestic audience could signal flexibility in upcoming talks with the U.S. and South Korea. He’s set to meet South Korean President Moon Jae-in on April 27 at a border village, possibly paving the way for an unprecedented summit with Trump in May or June.

Trump called Kim’s statement “very good news for North Korea and the World.” “Big progress!” Trump said in a tweet. “Look forward to our Summit.”

Later, he noted that North Korea would “shut down a nuclear test site in the country’s Northern Side to prove the vow to suspend nuclear tests.” A spokesman for Moon called Kim’s moves a positive sign.

Although U.S. and South Korean officials say Kim has expressed a willingness to discuss “denuclearization,” North Korea’s media has steered clear of the term. Kim’s remarks made no commitment to give up the estimated 60 nuclear bombs and the unknown number of ICBMs he already has.

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Shin Beomchul, a professor at the Korean National Diplomatic Academy, called Kim’s comments a “very carefully coordinated calculation to build hopes of the world that it’s open to changes that could possibly follow the summits.”

“It’s still hard to tell from the statement if it has genuine intent to denuclearize,” Shin said. “Contents-wise, there’s no real change in its position.”

Two U.S. officials who asked not to be identified said there was no reason not to believe Kim’s pledge was genuine. U.S. pressure had changed the calculus for Kim, one official said.

North Korea’s arsenal represents the achievement of three generations of Kims and is so central to the regime that its status as a “nuclear state” is enshrined in the constitution. The weapons provide a potent deterrent to any U.S.-led military action similar to what occurred in Iraq, Libya or Syria.

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Past negotiations with Kim’s late father, Kim Jong Il, over North Korea’s weapons program collapsed amid disputes over inspections, economic aid and U.S. security guarantees.

The Workers’ Party meeting expressed only general support for “worldwide disarmament.” “Our decision to suspend nuclear tests is part of the world’s important steps for nuclear disarmament and our republic will join global efforts to completely suspend nuclear tests,” Kim said.

North Korea has already effectively halted weapons tests since firing a missile in late November believed to be capable of reaching any city in the U.S. After that launch, which prompted the most restrictive United Nations sanctions yet, Kim declared his regime’s decades-long quest for nuclear weapons “complete” and opened talks with South Korea.

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Meanwhile, commercial satellite imagery of the Punggye-ri site has shown no recent evidence of major activity, according to the 38 North website, which monitors North Korea. Tunnels there have caved in after each of the country’s six nuclear tests, said Hong Tae-kyung, a professor of geophysics at Seoul’s Yonsei University.

“There’s even a possibility of radioactive leaks there,” Hong said. “Realistically, it’s highly unlikely they can be used for nuclear tests any more.”

Still, North Korea has been feeling the weight of economic sanctions and Kim’s statements to the party meeting signaled a desire to prioritize the development of his impoverished country. That shift that could make any offers of outside aid or sanctions relief more appealing in negotiations.

China’s Global Times newspaper, which is published by the Communist Party, called on Japan, South Korea and the U.S. to immediately lift all unilateral sanctions on North Korea. Foreign Ministry spokesman Lu Kang said in a statement that Kim’s promises would help promote a political settlement to the tensions.

Japan, however, expressed skepticism. Prime Minister Shinzo Abe told reporters Kim’s pledge wouldn’t change how Japan handles the regime, Kyodo News reported.

“We have made many promises with North Korea. We paid money on the condition that they would end a test facility and such,” Finance Minister Taro Aso told reporters in Washington. “But I remember that they just took our money.”