This Feb. 25, 2018 photo released by IHS Markit shows the Yongbyon experimental light water reactor in North Korea. Credit: DigitalGlobe | IHS Markit via AP

SEOUL, South Korea — Satellite imagery of a North Korean nuclear research site suggests improvements have progressed at a “rapid pace” in recent months, a report from a monitoring group said Wednesday, but the level of current operations at the facility remains unclear.

The analysis by the group 38 North, which closely follows North Korea affairs, offered a snapshot of the Yongbyon Nuclear Scientific Research Center on June 21 — nine days after North Korean leader Kim Jong Un signed a declaration to “denuclearize” after the Singapore summit with President Donald Trump.

The 38 North report said the satellite imagery leaves doubts about the Yongbyon reactor’s “operational status” because of reduced discharge of cooling water, steam emissions and other factors. But it concluded that uranium enrichment appears to be in progress.

Despite the lack of conclusive details on Yongbyon’s operations, the report raises questions over whether Kim has taken steps to curb North Korea’s nuclear program since the June 12 summit. It is also likely to bring new concerns from the Trump administration over how the North interprets the Singapore declaration.

North Korea has called for a “step-by-step” process of dismantling nuclear capabilities in exchange for rewards such as lifting international sanctions. Trump administration officials have insisted, in response, that no economic pressures can be eased until the North makes significant progress toward ending its nuclear program.

Defense Secretary Jim Mattis is scheduled to hold talks Thursday in Seoul with South Korean Defense Minister Song Young-moo. Secretary of State Mike Pompeo also said he plans to travel to Pyongyang soon for the first high-level meetings with Kim’s regime since the summit.

The 38 North report said the imagery points to work “continuing at a rapid pace” in recent months at the site, which contains a plutonium production reactor and an experimental light-water reactor for possible energy production.

The report also noted that any ongoing enhancements to the facility points to decisions at the top. “The North’s nuclear cadre can be expected to proceed with business as usual until specific orders are issued from Pyongyang,” the report said.

The improvements at the site since March include a nearly complete cooling tower and a four-story engineering office building. It said “there was is no visible evidence yet” to suggest that operations are underway at the experimental reactor.

But the report concluded that operations appear to be moving ahead at a uranium enrichment plant because of “roof staining” that suggests “water vapor coming from the six cooling units associated with gas centrifuge operations.”

During an earlier period of outreach with the West a decade ago, North Korea invited international journalists in 2008 to film the destruction of the cooling tower at the Yongbyon nuclear reactor, from which it had been harvesting plutonium to make its first bombs. But North Korea had a separate uranium enrichment facility believed capable of producing weapons-grade material.

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