A senior adviser to US Secretary of Defense James Mattis said it was not intended as a provocation, but acknowledged the type of exercise was the first of its kind in 20 years.
At the same time, Japan's Air Self Defense Force F-15s are taking part in simulated combat with US Navy F-18 fighters, the military added.
The US has been leading efforts to impose additional sanctions on North Korea, and has been urging China to put pressure on Pyongyang as its sole economic lifeline.
North Korea can already strike anywhere in Japan with missiles, raising concern in Tokyo that it could eventually be threatened by a North Korean nuclear strike.
Rumored Free Games Leaked by PlayStation Turkey?
Plus, this is only two games as there's usually at least five or six in every bunch, so we're still without a complete list. Sony has yet to include a PSVR game in their PlayStation Plus lineup since PlayStation VR first launched in October.
Japan's naval and air forces have launched a three-day joint military drill with U.S. aircraft carriers in the Sea of Japan amid tensions with North Korea over its missile and nuclear programs.
The joint training comes after North Korea successfully carried out three ballistic missile tests in a month. In total, about 300 Tomahawks have their sights trained on North Korea's nuclear test sites and underground facilities. If accurate, that yield would mean that North Korea is now in possession of a nuclear weapon twice as powerful as the atomic bomb dropped by the United States on Hiroshima, Japan, on August 6, 1945.
A South Korean TV viewer watches footage of North Korea "supreme leader" Kim Jong Un. The problem for North Korea is that the country's nuclear program does not yet appear capable of producing a bomb compact enough in size to be mounted on an intercontinental ballistic missile - making it a danger to other countries including the USA, though experts say that North Korea could launch a nuclear strike over the border with South Korea. Just as North Korea is reacting to American carriers and cruise-missile-equipped vessels in nearby waters, the U.S.is preparing for a scenario where Pyongyang acquires ICBMs.
"The Ronald Reagan and Carl Vinson Strike Groups were joined by the Japan Maritime Self-Defense Forces (JMSDF) for routine training to improve interoperability and readiness in the Indo-Asia Pacific", the US Seventh Fleet said on its Facebook page.