President Donald Trump boards Air Force One at Chennault International Airport in Lake Charles, La., following a visit with those helping with the impacted of Hurricane Harvey, Saturday, Sept. 2, 2017. AP Photo/Susan Walsh President Donald Trump issued a set of tweets Sunday morning attacking North Korea after the country appeared to conduct its sixth nuclear test.

"North Korea has conducted a major Nuclear Test. Their words and actions continue to be very hostile and dangerous to the United States," Trump tweeted.

Before the test, North Korea claimed that leader Kim Jong Un had inspected a hydrogen bomb meant for a new intercontinental ballistic missile. South Korea's military said Sunday that North Korea is believed to have conducted its sixth nuclear test after it detected a strong earthquake.

Trump also went after China's and South Korea's efforts to counter North Korea.

"North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success," Trump tweeted.

"South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"

On Tuesday, North Korea launched a missile that flew over the northern Japanese island of Hokkaido.

Japanese Prime Minister Shinzo Abe called the launch "an unprecedented, grave, and serious threat" that damaged the security of the region.

North Korea conducted its fifth test last year in September. If confirmed, the latest test would mark yet another big step forward in North Korean attempts to obtain a nuclear-armed missile.

The Associated Press contributed reporting to this article.