U.S. Secretary of State Rex Tillerson addressed the UN Security Council on what he calls the greatest threat to U.S. national security– North Korea. “Our message today is one this body has heard before and one we will continue to repeat: The United States will not allow the regime in Pyongyang to hold the world hostage,” Tillerson said.

Last month, Pyongyang launched a ballistic missile into waters near Japan but experts say it had the capacity to reach anywhere in the U.S. It was one of at least 20 ballistic missile launches North Korea conducted over the past year. “We believe that more can and must be done beyond enforcing the minimum requirements of Security Council Resolutions,” Tillerson said.

Tillerson particularly called on both Russia and China to increase pressure on North Korea. He says Russia is helping to pay for North Korea’s nuclear program and China is providing the country with oil.

Earlier this week, Tillerson said the U.S. would be willing to start diplomatic talks with North Korea without preconditions. But the White House dismissed the offer, saying talks can only take place after North Korea stops provoking its neighbors and takes sincere and meaningful steps toward denuclearization, as reported by CBS News.