By David Brunnstrom and Karen Lema MANILA (Reuters) -Secretary of State Antony Blinken assured the Philippines on Saturday that the United States would come to its defence if attacked in the South China Sea, seeking to allay concerns about the extent of the U.S. commitment to a mutual defence treaty. In meetings in Manila dominated by discussion on simmering U.S.-China tensions over the Taiwan visit of U.S. House of Representatives Speaker Nancy Pelosi, Blinken said a 70-year-old defence pact with the Philippines was “ironclad”. “An armed attack on Philippine armed forces, public vessels and a…