London, Mar 16 (IANS): North Korea has begun preliminary testing of one of its nuclear reactors at the Yongbyon research facility, according to new satellite imagery examined by Western experts.

The disclosure comes as preparations get underway for the summit between North Korean leader Kim Jong-un and South Korean President Moon Jae-in in April and ahead of Kim's planned meeting with US President Donald Trump in May, CNN reported on Friday.

A report by London-based intelligence analysts Jane's has said the imagery indicated that 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 non-condensable gases from the reactor's primary circuit", it said.

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

The reactor is linked to the power grid. Industry experts say that once operational, the ELWR would be able to produce about 25-30 megawatts, perhaps enough to power a town of some 50,000 inhabitants.

"In theory, if the reactor comes online and if it were diverted towards plutonium and tritium production, it could enable North Korea to expand its stock," CNN quoted Munks as saying.

Over the last year, Jane's and other research groups have identified increased activity in several parts of the Yongbyon site, 75 km north of Pyongyang.

Construction of the ELWR was completed in 2013 and is optimised for civilian electricity production, but it has "dual-use" potential and can be modified to produce material for nuclear weapons.