North Korea's sole-operating oil refinery has been up and running despite a series of media reports that China halted crude exports to the impoverished communist neighbor amid strained relations last year, a U.S. expert said Friday.

Joseph S. Bermudez Jr., chief analytics officer of AllSource Analysis, said in a report carried by the website 38 North of the Johns Hopkins School of Advanced International Studies that the North's Ponghwa Chemical Factory would not have been running if Beijing had halted crude exports.

Bermudez cited satellite imagery showing the refinery operational.

"Numerous reports during 2014-2015 have stated that China, North Korea's largest crude oil supplier, did not sell it crude oil during 2014, a development that would force North Korea's single operating oil refinery into caretaker status," Bermudez said in the report.

"Satellite imagery from 2014 and 2015, however, reveals that the facility has remained operational, though perhaps at somewhat lower levels than in the immediately preceding years, calling into question media reports of an oil cutoff from China," he said.

  Imagery indicates activity at the factory's rail loading and unloading facility, and construction activity within the factory, such as the building and maintenance of storage tanks and additions to several buildings, provides another indication that the facility remained operational, the expert said.

China has long been the main provider of food and fuel aid to the North.

But relations between Pyongyang and Beijing significantly soured after Chinese President Xi Jinping took office in late 2012 and the North carried out its third nuclear test a few months later. Xi is the first Chinese leader to visit South Korea before North Korea.

Xi has neither visited the North nor met with its young leader, Kim Jong-un, although he held a series of summit meetings with South Korean President Park Geun-hye.

The frayed relations between the North and China prompted speculation that China stopped crude supplies to the North. But widespread views are that even though crude exports could have been halted, Beijing has been providing it in aid.

Analyst say that China, which considers North Korea as something of a buffer zone, fears that pushing Pyongyang too hard could lead to its collapse, instability on its border and ultimately the emergence of a pro-U.S. nation next door. (Yonhap)