TOKYO (Reuters) - U.S. National Security Adviser H.R. McMaster told his Japanese counterpart on Sunday that Washington is firmly committed to defending Japan, including with its nuclear deterrent, following North Korea’s latest nuclear test.

McMaster made the assurance during a telephone call to Shotarou Taniuchi, the Director-General of the Japanese National Security Council, according to a government statement.

Under Japan’s alliance treaty with the United States, Washington has pledged to defend Japan. It has put Japan under its nuclear umbrella, meaning it could respond to any attack on Japan with atomic weapons.