North Korea may be preparing to launch a missile or space rocket, U.S. National Public Radio (NPR) reported.
The March 9 report was based on exclusive access to satellite photographs of North Korea's Sanumdong site, a facility that has been used by Pyongyang for the production of intercontinental missiles and space rockets in the past.
The photographs were taken by the firm DigitalGlobe a few days before U.S. President Donald Trump met in Vietnam with North Korean leader Kim Jong Un.
The images purportedly show rail cars, cranes, and trucks at the facility on February 22.
NPR quoted Jeffrey Lewis, a researcher at the Middlebury Institute of International Studies at Monterey, California, as saying "it looks like when the North Koreans are in the process of building a rocket."
The report comes shortly after the website 38 North and the Washington-based Center for Strategic and International Studies (CSIS) concluded the North may have resumed operations at a long-range rocket launch site at Sohae.
The February 27-28 summit between Trump and Kim ended without a joint statement or any agreement on North Korea's nuclear and missile programs.
Trump said on March 8 that he would be "surprised in a negative way" if North Korea resumed testing missiles.
"I would be very disappointed if I saw testing," he said.