WASHINGTON (Reuters) - U.S. government experts think North Korea could conduct a new missile test within days, in what would be its first launch since it fired a missile over Japan in mid-September, two authoritative U.S. government sources said on Tuesday.

FILE PHOTO: Trucks carry drones under a stand with North Korean leader Kim Jong Un and other officials during the parade celebrating the 70th anniversary of the founding of the ruling Workers' Party of Korea, in Pyongyang, October 2015. REUTERS/James Pearson

One of the sources, who did not want to be identified, said the United States had evidence that Japanese reports about the monitoring of signals suggesting North Korea was preparing a new missile test were accurate.

Both sources said U.S. government experts believed a new test could occur “within days.”

A Japanese government source said earlier on Tuesday that Japan had detected radio signals suggesting North Korea may be preparing another ballistic missile launch, although such signals were not unusual and satellite images did not show fresh activity.

South Korea’s Yonhap news agency, citing a South Korean government source, also reported that intelligence officials of the United States, South Korea and Japan had recently detected signs of a possible missile launch and have been on higher alert.

The U.S. officials who spoke to Reuters declined to say what type of missile they think North Korea might test, but noted that Pyongyang had been working to develop nuclear-tipped missiles capable of hitting the United States and had already tested inter-continental ballistic missiles.

Other U.S. intelligence officials have noted that North Korea has previously sent deliberately misleading signs of preparations for missile and nuclear tests. These have been in part to mask real preparations, and in part to test U.S. and allied intelligence on its activities.

After firing missiles at a rate of about two or three a month since April, North Korea paused its missile launches in late September, after it fired a missile that passed over Japan’s northern Hokkaido island on Sept. 15.

Last week, North Korea denounced U.S. President Donald Trump’s decision to relist it as a state sponsor of terrorism, calling it a “serious provocation and violent infringement.”

The designation allows the United States to impose more sanctions, though some experts said it risked inflaming tensions.

Trump has traded insults and threats with North Korean leader Kim Jong Un and warned in his maiden speech to the United Nations in September that the United States would have no choice but to “totally destroy” North Korea if forced to defend itself or its allies.

Washington has said repeatedly that all options are on the table in dealing with North Korea, including military ones, but that it prefers a peaceful solution by Pyongyang agreeing to give up its nuclear and missile programs.

To this end, Trump has pursued a policy of encouraging countries around the world, including North Korea’s main ally and neighbor, China, to step up sanctions on Pyongyang to persuade it to give up its weapons programs.

North Korea has given no indication it is willing to re-enter dialogue on those terms.

South Korean Unification Minister Chow Myoung-gyon told reporters on Tuesday there had been “noteworthy” movements from the North since its last missile launch, including engine tests, but there was no hard evidence of another nuclear or missile test.

“North Korea hasn’t been engaging in new nuclear or missile tests but recently we’ve seen them persistently testing engines and carrying out fuel tests,” he said. “But we need some more time to see whether these are directly related to missile and nuclear tests.”

Cho said North Korea may announce the completion of its nuclear program within a year, as it is moving more quickly than expected in developing its arsenal.

North Korea defends its weapons programs as a necessary defense against U.S. plans to invade. The United States, which has 28,500 troops in South Korea as a legacy of the 1950-53 Korean war, denies any such intention.