As President Trump prepares for his first meeting with South Korean President Moon Jae-in at the White House Thursday, his advisers believe there’s much more that the two nations can do together to get North Korea’s attention.

“We are adding pressure and have really only begun to do so,” a senior White House official told reporters. “It’s really the one approach that we haven’t tried yet — acute economic pressure on North Korea. That campaign is only now gathering momentum. And the president is determined to follow through with that and to see how it works.”

The North Korean regime has nuclear weapons and is working on development of an intercontinental ballistic missile, which the U.S. views as a direct threat.

North Korea conducted about 30 missile tests last year and detonated two nuclear devices, and the Trump official said former President Barack Obama didn’t begin to apply serious pressure on Pyongyang until his final year in office. There have been at least 14 missiles fired since Mr. Trump took office.

“It was only really over the course of 2016 that our prior administration began to apply acute pressure through those U.N. sanctions, security council resolutions,” the official said. “To say that pressure has not worked, it’s a little early to say that. There is plenty more pressure that could be brought to bear on North Korea in the form of U.N. sanctions, security council resolutions and also unilateral sanctions.”