North Korea claimed Monday the ballistic missile it test-fired a day earlier is capable of carrying a nuclear warhead.

The state-run Korean Central News Agency quoted North Korean leader Kim Jong Un as saying the country’s rocket program has transitioned to solid fuel. The missile used in the latest test traveled 300 miles before plunging into the Sea of Japan. The launch coincided with Japanese Prime Minister Shinzo Abe’s visit to the United States.

KCNA said Kim supervised the test of the Pukguksong-2 missile, which was fired early Sunday at an angle high enough so that it didn’t hit any of North Korea’s neighbors.

The test was the first since U.S. President Donald Trump took office and prompted him to reassure Abe.

“I just want everybody to understand and fully know that the United States of America stands behind Japan, its great ally, 100 percent," Trump said, urging Pyongyang to comply with U.N. resolutions outlawing ballistic missile tests.

During the presidential campaign, Trump vowed to take a tougher line with North Korea but there’s little he can do beyond upping pressure on China to intervene and beefing up defenses, neither of which has made much difference in the past.

White House policy adviser Stephen Miller said on CBS’ “Face the Nation” the U.S. will be “sending another signal very soon” in response to North Korea’s actions.

“That signal is when we begin a great rebuilding of the armed forces of the United States. President Trump campaigned on this,” Miller said. “President Trump has led the effort on this. And President Trump is going to go to Congress and ask them to invest in our military so once again we will have unquestioned military strength beyond anything anybody can imagine.”

North Korea declared the missile test a success. Protests were lodged by Japan and South Korea, which said the breached U.N. Security Council resolutions.

"[The missile launch] is not only an explicit and clear violation of related UNSC resolutions but also a grave threat to the peace and stability of the Korean Peninsula and the international community as a whole," Seoul's foreign ministry said in a statement.

North Korea has conducted a number of missile tests in recent months and a nuclear test in September that prompted international condemnation and a new round of sanctions.