Secretary of State Rex Tillerson wrapped up his first visit to Asia with a trip to Beijing Sunday, where he warned regional tensions with North Korea had reached "dangerous levels." On Saturday, North Korea tested a high-thrust rocket engine—the latest in a series of rocket and missile tests North Korea has carried out in recent weeks. During his Asia trip, Tillerson also suggested the U.S. may make a preemptive strike against North Korea. On Friday, President Trump tweeted, "North Korea is behaving very badly. They have been 'playing' the United States for years. China has done little to help!"