North Korea may be trying to restart a nuclear bomb fuel reactor, just five months after it was shuttered, a U.S. research institute said Thursday. The U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies said it found possible signs in satellite imagery from Dec. 24 through Jan. 11 that indicate the reactor is in the early states of being restarted at the 5-megawatt Nyongbyon reactor. Such signs include hot water drainage from a pipe at a turbine building that points to steam from the reactor as well as snow-melt on the roofs of the reactor and turbine buildings. However, it’s too soon to tell if North Korea is definitively in the process of restarting its nuclear plant, according to the institute. The news comes after the U.S. tightened sanctions on North Korea after blaming Kim Jong Un’s government for the crippling hacking attacks on Sony Entertainment.