SEOUL, July 18 (Reuters) - For the first time since the 1980s a U.S. nuclear-armed ballistic missile submarine (SSBN) is in South Korea, a senior U.S. official said on Tuesday, as the allies launched talks to coordinate responses in the event of a nuclear war with North Korea.

White House Indo-Pacific coordinator Kurt Campbell announced the long-expected visit while he was in Seoul for the first Nuclear Consultative Group discussion with South Korean officials.