Foreign banks will have to decide whether to work with the U.S. or do business with North Korea, President Trump said Thursday at the United Nations General Assembly during a meeting with South Korean President Moon Jae-in and other world leaders. He is enacting an executive order to target entities that continue to engage in trade with North Korea.

BREAKING: POTUS announces executive order that expands authorities to target individuals, companies that facilitate trade with North Korea. pic.twitter.com/mKXaG9dUZ1 — ABC News (@ABC) September 21, 2017

"A new executive order will cut off sources of revenue that fund North Korea's efforts to develop the deadliest weapons," the president said.

The calls are already being answered, it seems, as Trump noted that China has ordered its central bank to cease all trade with North Korea, a "brutal" regime that does not respect its own citizens.

Trump's warning to companies and individuals who want to do business with the regime comes a couple of days after his strong rebuke of "Rocket Man" Kim Jong Un. If the U.S. and her allies feel threatened by North Korea and its continued ballistic missile tests, they can expect a response.

"The United States is ready, willing and able, but hopefully this will not be necessary," the president warned.

Japanese Prime Minister Shinzo Abe was also at Thursday's meeting and he thanked Trump for his leadership in answering North Korea's aggression.

At the end of the meeting, a reporter asked Trump if dialogue was still possible with North Korea.

"Why not," he said.