(CNN) New satellite imagery examined by Western experts suggests North Korea has begun preliminary testing of one of its nuclear reactors at the Yongbyon research facility. The disclosure comes as preparations get underway for the summit between North Korean leader Kim Jong Un and South Korean President Moon Jae-in next month -- and ahead of Kim's planned meeting with President Trump in May.

A report by intelligence analysts Jane's says the imagery indicates the experimental light water reactor, known as an ELWR, could become operational "with little warning" as early as later this year.

According to Jane's, an image from February 25 shows an emission rising from the reactor's stack that "implies testing of the machinery at the site." The stack is "intended to vent noncondensable gases from the reactor's primary circuit," Jane's says.

What is unclear at this stage is whether North Korea plans for the reactor to contribute to electricity generation or its weapons program.

Rob Munks, editor of Jane's Intelligence Review, says the light-water reactor "could be used for civilian electricity generation -- its stated purpose -- or diverted towards the nuclear program."

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