Pentagon sends missile defences to Guam as North Korea 'approves nuclear attack on US' He said those actions had threatened the interests of South Korea and Japan, but he also cited their direct threats against Guam, an American territory in the Pacific, Hawaii and West Coast of the United States. Shortly after Mr Hagel spoke, the Pentagon said it was deploying a Terminal High Altitude Area Defense system (THAAD), which includes a truck-mounted launcher, interceptor missiles, an AN/TPY-2 tracking radar and an integrated fire control system. "The United States remains vigilant in the face of North Korean provocations and stands ready to defend U.S. territory, our allies, and our national interests," a Pentagon spokesman said. The news that the ground-based system would be in place in the coming weeks came after two Aegis anti-missile destroyers were sent to the western Pacific to intercept any North Korean strike against US or allied targets. Despite North Korea's highly-publicised missile tests, relatively little is known about the actual size and capabilities of its arsenal. The announcement came after Pyongyang shut down the last shared link with the South by refusing entry to almost 500 South Korean workers who work in a cross-border industrial park. Zhang Yesui, the deputy foreign minister, outlined Beijing's "serious concern about the present situation," and added that it expects the escalation of tension to cease. "All sides must remain calm and exercise restraint and not take actions which are mutually provocative and must certainly not take actions which will worsen the situation," said the foreign ministry. The Kaesong complex lies six miles inside North Korea and houses 123 South Korean companies and their 53,000 North Korean workers. A key source of foreign currency for Pyongyang, generating some $100 million (£66 million) each year, it has never been closed, weathering the aftermath of the 2009 nuclear tests and the shelling of Yongpyeong island the following year. A graphic showing what North Korea's missile capabilities are believed to be, though relatively little is known about the rogue state's nuclear arsenal. North Korea said the 861 South Koreans who were at the site on Wednesday were free to return home, but with no replacements arriving for their shifts, only 33 did so. Workers emerging from Kaesong on Wednesday said production was continuing. With Reuters and Agence France-Presse