A new report says North Korea is avoiding United Nations sanctions by using China as an intermediary.

The Congressional Research Service, the public policy research arm of the U.S. Congress, said in a report that due to this, sanctions on North Korea have been rendered ineffective. The sanctions ban the North from trading weapons of mass destruction and from importing luxury goods.

The report also said that China is failing to actively cooperate with the U.N. sanctions because it hopes to maintain the status quo in North Korea and to prevent the entry of North Korean refugees that could result from a collapse of the North.

The report said that because China has taken a minimal approach to implementation of sanctions on the North, it has proven difficult to strengthen measures any further in the U.N. context.

The U.N. Security Council placed the sanctions on North Korea to penalize it for its nuclear tests in 2006 and 2009.