South Korean intelligence officials have reportedly seen signs of new activity at North Korean nuclear sites that the country previously pledged to dismantle.

Yonhap News Agency reported Tuesday that workers could be seen replacing a roof and installing a new door at the Tongchang-ri nuclear launch site, which North Korean officials promised last year to dismantle following an initial summit between President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE and Kim Jong Un, according to Reuters.

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It's not clear whether the new activity was detected before or after Trump's second summit with Kim, which ended last week without a new agreement between the two leaders for more concessions by either side.

Initial efforts to dismantle the nuclear site began briefly last year, but were halted within a month, according to Reuters. Kim subsequently promised during a summit with South Korean President Moon Jae-in to continue deconstruction of the facility.

In November, however, North Korean officials indicated that progress on dismantling the Tongchang-ri facility and others could be reversed if U.S. sanctions on the country's economy were not lifted, which Trump refused to do at last week's summit.

"If the U.S. keeps behaving arrogantly without showing any change in its stand, while failing to properly understand our repeated demand, the DPRK may add one thing to the state policy for directing all efforts to the economic construction adopted in April and as a result, the word 'pyongjin' may appear again," the country's foreign ministry said last year.

Secretary of State Mike Pompeo Michael (Mike) Richard PompeoOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Overnight Defense: House Democrats unveil stopgap spending measure to GOP opposition | Bill includes .6B for new subs | Trump issues Iran sanctions after world shrugs at US action at UN Navalny calls on Russia to return clothes he was wearing when he fell ill MORE reportedly said Monday at a news briefing that the Trump administration hopes to send a delegation to North Korea in the coming months, while adding that they had made "no commitment yet" to do so.