The United States is investigating a number of Chinese companies for suspected breaches of sanctions on North Korea, and Chinese banks and firms should understand that dealing with North Korea is "risky," a senior U.S. official said on Wednesday.

China said it opposed any country using its own laws for "long-arm jurisdiction," after the United States on Monday sanctioned China's Dandong Hongxiang Industrial Development Co. for using front companies to evade sanctions on North Korea's nuclear weapons and ballistic missile programs.

It was the first time the United States has taken such a step against a Chinese firm, and Daniel Fried, sanctions policy coordinator at the U.S. State Department, told a U.S. Senate hearing the action should serve as a warning. He said it would be better if China took such actions itself.