US officials say North Korea's sixth nuclear test could come as early as Saturday morning.
Officials and other sources said the reclusive nation had placed a nuclear device in a tunnel, which could be detonated by the end of the week, according to Steve Herman, White House bureau chief of Voice of America News.
The suspicion is also corroborated by four weeks of "high levels of activity" at the Punggye-ri nuclear-test site, according to 38 North, a research group from the US-Korea Institute at Johns Hopkins University.
The research group's findings included new commercial-satellite imagery that showed the location of the tunnel, where four of North Korea's recent nuclear tests were also initiated, in addition to other evidence of an imminent test.
According to their analysis, water being pumped from the suspected tunnel was being soaked to the ground elsewhere, which may indicate that the tunnel was being prepped for testing devices. Additionally, tracks from footsteps and vehicles were visible from the melting snow. Identifying the exact equipment being used proved to be difficult, however, due to what appeared to be netting that covered the area.
"We have no comment at this time but we will be watching closely," a defense official said to VOA.
The suspected detonation date, April 15, is of importance for the country, considering that it marks the 105th birth anniversary of Kim Il Sung, North Korea's founder. The nation has in the past conducted other extravagant military displays on special dates — on April 2012, the country to fired a failed long-range rocket prior to the "100th Day of the Sun."
The report follows North Korea's message to foreign journalist to prepare for a "big and important event" earlier this week. On Tuesday, several journalists were allegedly woken up before dawn and were told to get ready with no other information or details.
Around 200 journalists were then reported to have been told to leave their lighters, cell phones, and laptops, before being placed in buses to be transported to a different location for the event. So far, reports from the country have remained scant.
Amid the tensions, a US Air Force WC-135 Constant Phoenix was also reported to have arrived in neighboring Japan on April 7. The aircraft specializes in radioactive debris detection and is also known as a "nuke-sniffer."