Japan detected radio signals that my indicate that North Korea may be preparing for a new ballistic missile launch, a government source said on Tuesday.
It later added however that such signals are not unusual and satellite images did not show fresh activity.
“This is not enough to determine (if a launch is likely soon),” the source told Reuters.
Japan’s Kyodo news agency reported late on Monday that the Japanese government was on alert after catching such radio signals, suggesting a launch could come in a few days. The report also said the signals might be related to winter military training by the North Korean military.
South Korea’s Unification Minister Cho Myoung-gyon confirmed that his country had also detected such signals.
He told reporters on Tuesday there have been “noteworthy” movements from the North since its last missile launch in mid-September, 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,” said Cho at a media event in Seoul.
“But we need some more time to see whether these are directly related to missile and nuclear tests.”
The South Korean news agency Yonhap cited a government source as saying: "It's true that active movements have been detected at a North Korean missile base. Signs like those spotted Monday have recently been detected frequently."
"We need to watch a while longer before determining whether the North is preparing a missile launch or gearing up for (its own) winter drill that starts Friday,” he added.
A South Korean defense ministry spokesman declined to comment on the report, but similar accounts from Tokyo caused a temporary slump on the stock exchange there.
After firing missiles at a pace of about two or three a month since April, North Korean missile launches paused in September, after it fired a rocket that passed over Japan’s northern Hokkaido island.
North Korea is pursuing its nuclear weapons and missile programs in defiance of UN Security Council sanctions and has made no secret of its plans to develop a missile capable of hitting the US mainland. It has fired two missiles over Japan.
The South Korean government source also said 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.
Asked about the media reports, Pentagon spokesman Colonel Robert Manning told reporters the US continued to watch North Korea very closely.
“This is a diplomatically led effort at this point, supported by military options,” he said.
“The Republic of Korea and US alliance remains strong and capable of countering any North Korean provocations or attacks.”
Two US government sources familiar with official assessments of North Korean capabilities and activities said that while they were not immediately familiar with recent intelligence suggesting that North Korea was preparing to launch a new missile test, the US government would not be surprised if such a test were to take place in the very near future.
Other US intelligence officials noted North Korea has previously sent deliberately misleading signs of preparations for missile and nuclear tests, in part to mask real preparations, and in part to test US and allied intelligence on its activities.
South Korea’s Cho said North Korea may announce the completion of its nuclear program within a year, as it is moving more faster than expected in developing its arsenal.
Tensions are expected to spike again as the US and South Korea kick off a large-scale air force drill on Monday in a new show of force against the North.
The five-day exercise, Vigilant Ace, involves 12,000 US personnel and an unspecified number of South Korean service members flying more than 230 aircraft including F-22 Rapter stealth fighters and other cutting-edge weapons at US and South Korean military bases.
Pyongyang routinely condemns such exercises, labeling them preparation for war.
The US last week unveiled fresh sanctions that target North Korean shipping, raising pressure on Pyongyang to abandon its nuclear program.
Pyongyang condemned the move as a "serious provocation" on Wednesday and warned that sanctions would never succeed.
North Korea defends its weapons programs as a necessary defense against US plans to invade. The United States, which stations 28,500 troops in South Korea, a legacy of the 1950-53 Korean war, denies any such intention.