China completely cut off supply of crude and processed oil to North Korea for four months immediately after North Korea's second nuclear test in 2009.

It seems China quietly imposed separate sanctions on North Korea independently of UN Security Council resolutions.

Beijing could take similar measures this time as North Korea continues to threaten regional peace with its nuclear ambitions.

Chinese crude oil is supplied to Sinuiju in North Korea through pipelines from the oil reserve in Basan on the outskirts of Dandong near the border. The processed oil is delivered by ship.

According to Chinese Customs data, China exported no crude or processed oil to the North between July and October 2009.

The North carried out its second nuclear test in May 2009, and in June the UN Security Council adopted the resolution that imposed sanctions on North Korea.

Then-Chinese Primier Wen Jiabao visited Pyongyang to meet Kim Jong-il in October that year, and Beijing resumed oil supplies only after he met Kim Jong-il there.

A source in Beijing said, "There had been times when China cut its oil supply to North Korea for about a month early in the year for maintenance work on the pipeline, but a four-month interruption was unprecedented. It seems that China took strong steps to pressure the North."

Due to the interruption, Chinese crude oil exports to North Korea dropped by 60.4 percent from US$414.31 million in 2008 to $164.19 million in 2009. Exports of processed oil also fell 61.4 percent from $120.07 million in 2008 to $46.36 million.

China had several times cut off oil supply to North Korea for three days when Pyongyang left the Treaty on the Non-Proliferation of Nuclear Weapons in early 2003, and for three months in early 2004, when it boycotted six-party nuclear talks.

