The United States has warned China it will blacklist Chinese companies and banks that do illicit business with North Korea if Beijing fails to enforce U.N. sanctions against Pyongyang, according to senior State Department officials.

The tougher U.S. approach reflects growing impatience with China and a view that it has not strictly enforced existing sanctions to help curb Pyongyang's nuclear program, which a U.S. policy of both sanctions and diplomacy has failed to dent.

U.S. Deputy Secretary of State Antony Blinken gave the message to Chinese officials in meetings in Beijing in October after North Korea conducted its fifth and largest nuclear test, the officials said.