Lighthizer, who campaigned with President Trump, serves as an unofficial adviser. He was reportedly passed over for Treasury secretary, but he remains close to the president. Lighthizer says U.S. trade with China has largely benefited an adversary who has engaged in stealing trade secrets and other malicious actions.

President Donald Trump said on Sunday the sweeping tariffs that he has imposed on Mexico, Canada and China may cause "some pain" for Americans, as Wall Street and the largest U.S. trading partners signaled hope that the trade war would not last long.

Amid warnings of price increases, Canada moved quickly to retaliate, China said it had planned countermeasures, and Mexico said it would soon unveil its response.