China on Thursday ordered North Korean-owned businesses to shut down by January, cutting foreign revenue for the isolated North under UN sanctions imposed over its nuclear and missile programs.

North Korean businesses and ventures with Chinese partners must close within 120 days of the Sept. 11 approval of the latest sanctions, according to the Ministry of Commerce. That would be early January.

China is North Korea’s main trading partner, making Beijing’s cooperation essential to the success of sanctions imposed in an effort to top the North’s pursuit of weapons technology. China has long been North Korea’s diplomatic protector but has gone along with the latest penalties out of growing frustration with leader Kim Jong Un’s government.

The latest round of sanctions approved by the UN Security Council ban member countries from operating joint ventures with North Korea.

The sanctions also ban sales of natural gas to North Korea and purchases of the North’s textile exports, another key revenue source. They order other nations to limit fuel supplies to the North.

North Korean companies operate restaurants, trading outfits and other ventures in China, helping to provide the North with foreign currency.

China, which provides the bulk of North Korea’s energy supplies, announced Saturday it would cut off gas and limit shipments of refined petroleum products, effective Jan. 1. It made no mention of crude, which makes up the bulk of Chinese energy supplies to North Korea and is not covered by the UN sanctions.

China also has banned imports of North Korean coal, iron and lead ore, and seafood since early September.

On Thursday, the Ministry of Commerce defended its recent imports of North Korean coal as permitted by UN sanctions.

A ministry spokesman, Gao Feng, said imports that were reported in August trade data were allowed by a “grace period” for goods that arrived before the UN ban took effect.

The imports are “in line with the (UN) resolution,” Gao said.