WASHINGTON (AP) – U.S. researchers see further signs from satellite imagery that North Korea is looking to produce more plutonium for nuclear weapons.

The activity seen at the Nyongbyon nuclear complex comes amid a flurry of weapons-related tests by North Korea.

The website 38 North says that commercial satellite imagery taken Monday shows a rail flatcar at radiochemical laboratory where North Korea separates weapons-grade plutonium from waste from a nuclear reactor.

It says tanks or casks on the flatcar could be used to supply chemicals or haul out waste products. In recent weeks, exhaust plumes seen at the laboratory also suggest that nuclear reprocessing could be in the works.

South Korean and U.S. officials said Friday that North Korea conducted a failed missile test, the latest in a series of provocations.