The U.S. military has begun moving a missile defense system to South Korea after North Korea launched four ballistic missiles into waters off Japan early Monday. The Terminal High Altitude Area Defense system, scheduled to be fully deployed by the end of the year, is seen as a hostile threat by China and North Korea but is described as a defensive system by the U.S. military. The system is meant to intercept short- and medium-range ballistic missiles, the U.S. military said in a statement Monday. “Continued provocative actions by North Korea, to include yesterday’s launch of multiple missiles, only confirm the prudence of our alliance decision last year to deploy THAAD to South Korea,” Adm. Harry Harris said in the statement. South Korea’s acting president, Hwang Kyo-ahn, had called for quick deployment of the system after the launch on Monday in order to “acquire a defense system against North Korea’s nuclear missiles,” Reuters reported. A South Korean official who spoke on condition of anonymity told the Associated Press that the country has received launchers for the system, though he didn’t reveal how many. North Korea’s test launch Monday has renewed fears about the country’s nuclear capabilities, with Japanese Prime Minister Shinzo Abe warning of a “new kind of threat.” Three of the missiles reportedly landed in Japan’s exclusive economic zone, an offshore area where the country has rights to explore resources.