NEW YORK — A new report from the UN's nuclear watchdog expresses "grave concern" that North Korea is continuing to develop its nuclear program, despite the regime's commitment to work towards denuclearization following June's summit in Singapore.

The International Atomic Energy Agency (IAEA) wrote in the report published Monday that inspectors have not been granted access to key nuclear sites in North Korea, including the research facility at Yongbyon. The agency used satellite imagery and open-source reports to conclude that construction has resumed or continued at several locations in and around the site.

The agency, based in Geneva, said the North's continued nuclear activities constitute "clear violations of relevant UN Security Council resolutions" and "are deeply regrettable."

"The continuation and further development of the DPRK's nuclear programme and related statements by the DPRK are a cause for grave concern," the report said, referring to the Democratic People's Republic of Korea, the North's official name. The agency said inspectors would be able to move quickly to inspect the North's nuclear sites if inspectors are granted access, reiterating comments by the agency's director last year.

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In April, North Korean leader Kim Jong Un signed an agreement known as the Panmunjom Declaration with South Korean President Moon Jae-in, in which both parties committed to the "complete denuclearization of the Korean peninsula." Kim reaffirmed that agreement during his summit with President Trump in Singapore in June, but has shown no willingness to unilaterally dismantle its nuclear program in the months since.

In an interview with Reuters on Monday, Mr. Trump took credit for North Korea halting its nuclear and ballistic missile testing.

"I stopped (North Korea's) nuclear testing. I stopped (North Korea's) missile testing. Japan is thrilled. What's going to happen? Who knows? We're going to see," he said. Mr. Trump said he would "most likely" meet with Kim for a second time.

Earlier this month, Secretary of State Mike Pompeo said that the North has not yet lived up to its pledge to denuclearize.

"To the extent they are behaving in a manner inconsistent with that, they are in violation of one or both the UN Security Council resolutions, we can see we still have a ways to go to achieve the ultimate outcome we're looking for," Pompeo told reporters ahead of a security forum in Malaysia.

Pamela Falk contributed reporting.