By Yi Whan-woo

The international community remains clueless over the amount of oil North Korea imports, meaning it could suffer a setback in toughening sanctions on Pyongyang even if it manages to impose an oil embargo.

The Central Intelligence Agency (CIA) said North Korea imported 70,000 barrels a day in 2013 in its recently updated "The World Factbook."

That amounts to approximately 4.12 million tons per year.

The Tokyo Shimbun reported that North Korea set up a plan in April to build oil reserves that can hold up to 1 million tons.

Such capacity is about two thirds of North Korea's annual imports of crude oil and petroleum products, which is estimated to be 1.5 million tons, according to the newspaper.

The Korea Trade Investment Promotion Agency (KOTRA), citing its 2015 data, said North Korea's oil imports were only 500,000 tons per year.

Diplomatic sources varied in their views, too. Some speculated that Pyongyang's annual purchase of crude oil and petroleum products ranged from 1.5 million tons to 2 million tons, while others estimated the amount to be less than 600,000 tons.

Analysts attributed the lack of credible data to China's unwillingness to cooperate in tightening international sanctions on the North.

Beijing is believed to be responsible for over 90 percent of Pyongyang's oil imports, but it has been against disclosing the relevant amounts.

"The U.N. Security Council (UNSC) will need to figure out how much oil North Korea gets from abroad as precisely as possible so that it can better visualize a plan for an oil embargo," said Yang Moo-jin, a professor at the University of North Korean Studies. "I'm extremely concerned that North Korea, as it did before, will exploit loopholes in the UNSC sanctions, unless China cooperates."

An Chan-il, the head of the World Institute for North Korea Studies, speculated that China, in addition to its oil exports to North Korea, may be offering extra oil for free to the impoverished regime.

"It will be extremely difficult to track such a hidden deal unless China voluntarily shares the relevant records," he said.

The experts said that China has more than fear of collapse of the Kim Jong-un regime in its opposition toward international efforts toward cutting oil supplies to North Korea.

Some claimed that it will be "too costly" for China to clean up and refurbish the oil pipeline to North Korea if the oil supply is suspended for a long time.

The crude oil transported to North Korea contains paraffin wax, a colorless solid derivable. It will harden, and left stuck inside a pipeline will block it eventually if oil does not continue to flow, according to Yang.

Paik Hak-soon, a senior researcher at the Sejong Institute, said China may be worried that Russia is replacing Beijing's role as Pyongyang's largest patron if oil trade is suspended.

"About 10 percent of North Korea's oil imports is believed to be from Russia. Beijing apparently will not want Moscow expanding its influence on Pyongyang, especially considering the Kim regime's role as a buffer zone against U.S. influence," he said.