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SEOUL, South Korea — North Korea’s promise to shut down its main nuclear weapons test site by the end of May is a significant symbolic gesture, but the move will have little impact on Kim Jong Un's existing nuclear and ballistic missile programs, according to experts.

The North Korean leader agreed to close the Punggye-ri nuclear test site during his summit last week with South Korean President Moon Jae-in, Moon’s office announced Sunday.

Kim and Moon also issued a joint declaration Friday promising the “complete denuclearization” of the Korean Peninsula by the end of 2018.

What precisely that means has yet to be determined, but the closing of testing facilities such as Punggye-ri would almost certainly be required under even a loose interpretation of denuclearization.

Pyongyang has already demonstrated that it has a credible nuclear deterrent, and the dismantling of Punggye-ri will not affect any weapons it already possesses.

The ongoing utility of Punggye-ri is also unclear. Numerous analysts have concluded, based on satellite photos taken before and after a nuclear test carried out by North Korea in September, that portions of the site had collapsed and were no longer useful. Pyongyang claimed it was the successful demonstration of a hydrogen bomb.

“If reports are true that the tunnels have collapsed, then the test site would be useless for future nuclear tests anyway, so it would just be a symbolic gesture to close it down,” said Duyeon Kim, visiting senior fellow at the Korean Peninsula Future Forum, a nonpartisan think tank in Seoul. “It’s not a serious or sincere gesture to denuclearize.”

The possible closure of Punggye-ri was telegraphed by Kim Jong Un nearly a week before his summit with Moon.

“We no longer need any nuclear tests, mid-range and intercontinental ballistic rocket tests, and … the nuclear test site in the northern area has also completed its mission,” the dictator said in a statement on the state-run Korean Central News Agency on April 21.

Kim claims to have developed an intercontinental ballistic missile that's capable of reaching the U.S. mainland.

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In his New Year's Day address, Kim claimed that "a nuclear button is always on my desk" and the "entire United States is within range of our nuclear weapons." However, analysts say that based on the current evidence it's hard to prove or debunk North Korea's claim that it could hit targets such as New York or Washington.

If Punggye-ri were closed permanently, it may have an impact on North Korea’s ability to conduct further testing in the short term, but wouldn’t substantially affect their existing weapons program.

A South Korean official shows a map featuring the location of an artificial earthquake detected from North Korea's Punggye-ri nuclear test site on Sept. 3, 2017. YONHAP / EPA

“I wouldn't be surprised if they are already digging a new test site or if they decide to forgo explosive tests" and instead carry out nuclear tests in labs, Duyeon Kim said. “Advanced nuclear states don’t need to conduct explosive tests after a certain point, so Pyongyang might be trying to show it is a part of that nuclear club.”

In September, Punggye-ri was the site of North Korea's sixth and most powerful test.

Independent experts continue to debate the type and the size of the weapon used during that test, but the U.S. Air Force Technical Applications Center, which monitors and assesses nuclear activity worldwide, reportedly estimated the weapon’s magnitude to have been 70 to 280 kilotons.

Such a weapon would be as much as 18 times more devastating than the atomic weapon used to destroy Hiroshima in 1945.