The crew of a Cathay Pacific flight over Japan saw a test of ballistic missiles from North Korea last week, the airline said.
The airline told the BBC that the crew flying from San Francisco to Hong Kong saw "what is suspected to be the re-entry" of a nuclear missile from North Korea during a test.
Last week, the North Korean regime tested an intercontinental ballistic missile (ICBM), the first test of its kind in more than two months, which could reach any city within the US. UU The regime praised the missiles as their "most powerful".
The details of the test remain unclear, with a US official saying that the missile failed to re-enter the Earth's atmosphere: the key problem of the communist country's nuclear program.
Without perfecting the "re-entry" technology, such missiles represent little danger as they fall apart before re-entering the Earth.
Continued nuclear weapons tests and hostile rhetoric have increased tensions in the region, with key US allies preparing for the possibility of a total war.
The United States and South Korea began a mbadive combined air force exercise on Monday following threats from the North. A five-day exercise called Ace Vigilante involves hundreds of planes and two dozen stealth aircraft.
The Ministry of Defense of South Korea said the practice aims to improve the capacity of the allies for war and preparation.
the exercise, saying that the United States was "begging for nuclear war" and will push the region "to the brink of nuclear war," the BBC reported. He also said that he "will seriously consider" an answer contrary to the military exercise.
The Associated Press contributed to this report.