SEOUL, South Korea — New satellite images and firsthand accounts from former political prisoners and former jailers in North Korea have confirmed the enormous scale and bleak conditions of the penal system in the secretive North, according to a report released Wednesday by the human rights group Amnesty International.

Former inmates at the political labor camp at Yodok, North Korea, said they were frequently tortured and had been forced to watch the executions of fellow prisoners, the report said, noting that the North’s network of political prisons is estimated to hold 200,000 inmates.

“North Korea can no longer deny the undeniable,” said Sam Zarifi, the Asia Pacific director of Amnesty International. “For decades, the authorities have refused to admit to the existence of mass political prison camps. These are places out of sight of the rest of the world.” The report says that almost all of the human rights protections that international law has tried to set up for the past 60 years “are ignored.”