North Korea could be preparing to test a submarine-launched ballistic missile, U.S. researchers say, after a cylindrical object resembling one of the country’s advanced weapons was spotted in satellite imagery of a key testing area taken Thursday.

Researchers with the North Korea-watching 38 North think tank published the results of their analysis Friday after spotting the white object at a shipyard in Sinpo, South Hamgyong province, on the country’s eastern coast. The object, which measured about 11.5 meters long and 1.4 meters wide and appeared to match the dimensions of Pyongyang’s Pukguksong-3 SLBM, was observed near an apparent truck-mounted crane.

“While this could indicate preparations for a forthcoming test, it may be unrelated as well,” the researchers wrote, noting that in September 2020, a similar white, cylindrical object of comparable size was observed, though no test took place around that time.