BEIJING -- The United States needs China's help with North Korea, but President Trump signed an executive memo on Monday that is sure to anger the Chinese.

The order calls for an investigation into whether China stole American intellectual property.

In response, the Chinese government used a strongly worded editorial in state run China Daily newspaper accused Mr. Trump of "exploiting trade as a bargaining chip" -- one that will "poison the overall China-U.S. relationship."

China has repeatedly warned Mr. Trump not to use trade as a means to force stronger action on North Korea. China accounts for 90 percent of North Korea's trade and has been reluctant to punish the regime economically for fear of collapse.

But on Monday, China issued an order banning all imports of North Korean coal, iron ore and seafood -- in compliance with tough new U.N. sanctions.

Meanwhile, Marine Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, began a tour of Asia meeting to reassure South Korean president Moon Jae-in.

Gen. Dunford says the U.S. still prefers diplomacy to force, but that the U.S. is ready to use the full range of its capabilities to respond to any attack.

The U.S. staged joint military exercises Monday with Japan and has also said it will go ahead with joint military exercises with South Korea in the region next week -- something that both China and North Korea oppose.

Kim Jong Un's regime continued its defiance, claiming 3.5 million North Koreans have volunteered to join its army, and in a new threat warned that even an accidental event could become a nuclear war on the Korean peninsula.

North Korea did announce Monday that Kim Jong Un has been briefed on military plans to launch four missiles toward Guam, but that he plans to wait. U.S. Defense Secretary James Mattis said Monday that the U.S. will shoot down any North Korean missiles heading toward Guam.