Nuclear-armed North Korea says it has completed its first military spy satellite and leader Kim Jong Un has approved final preparations for the launch.
The submarine visit is also seen as a way to reassure South Korea and quell talk in Seoul of developing homegrown nuclear weapons.
North Korea unveiled new, smaller nuclear warheads and vowed to produce more weapons-grade nuclear material to expand its arsenal.
US Indo-Pacific Command said the latest launches did not pose an immediate threat to US personnel or their allies.
The North's ballistic missiles are banned under United Nations Security Council resolutions and the launch drew condemnation from governments in Seoul, Washington and Tokyo.
Explosives left over from the 1950-1953 Korean War have long been a danger to citizens in both Koreas.
The sister of North Korean Supreme Leader, Kim Jong Un, warned that if the US interfered with North Korea's missile tests, it would be taken as a 'declaration of war.'
"No," Biden said when asked by reporters at the White House if he was currently discussing joint nuclear exercises with South Korea.
Pak Jong Chon was noticeably absent in photos released on Monday of Kim's New Year's Day visit to the Kumsusan Palace of the Sun.
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