For his first official trip abroad, Mattis began a two-day visit with longtime US ally South Korea on February 2, 2017. He warned North Korea that "any attack on the United States, or our allies, will be defeated", and any use of nuclear weapons would be met with an "effective and overwhelming" response from the United States. During a press conference in London on March 31, 2017 with the British secretary of state for defence, Michael Fallon, Mattis said North Korea was behaving "in a very reckless manner" and must be stopped. During a Pentagon news conference on May 26, Mattis reported the US was working with the UN, China, Japan, and South Korea to avoid "a military solution" with North Korea. On June 3 Mattis said the United States regarded North Korea as "clear and present danger" during a speech at the international security conference in Singapore. In a June 12 written statement to the House Armed Services Committee Mattis said North Korea was the "most urgent and dangerous threat to peace and security". On June 15 Mattis said the US would win a war against North Korea, but "at great cost".