Paul Whelan, the American who spent five and a half years wrongfully detained in Russia, revealed Sunday that he had passed to Western officials information he received from fellow prisoners who were fighting for Russia on the frontlines in Ukraine.

“The prisoners from the camp that went to the frontline, they had communication. And they would communicate with us. And the communication from them I was passing back to the four governments,” Whelan said on CBS’ ‘Face the Nation,’ referring to the US, the United Kingdom, Canada and Ireland — the four countries with which he holds citizenship.

Whelan added that he and others were able to communicate with former prisoners through “burner” phones that they could acquire even while at the Russian labor camp in Mordovia.

“Through illegal cell phones,” Whelan said. “Yeah, we had burner phones.”

Whelan added that the guards “looked the other way” in exchange for goods such as cigarettes.

“A Russian prison guard gets three, four hundred dollars a month. You give him a carton of cigarettes and you can do just about anything you want,” Whelan added.

During his years of detention, consular officials from the four governments would regularly meet with Whelan to check on him and provide updates on efforts to secure his release.

Whelan said that 450 prisoners from his camp went to fight in Ukraine as part of recruiting efforts by mercenary outfits including the Wagner Group, which signed up tens of thousands of prisoners from jails across Russia to bolster Russia’s brutal invasion. His camp was primarily made up of young men from central Asian countries such as Tajikistan, Uzbekistan and Kyrgyzstan, Whelan said.

“From my camp, 450 went. I knew all of them. Some of them are dead. Some have arms and legs missing. They’ve all got some sort of PTSD. They went through a traumatic experience,” he said. “They were used on the frontlines to walk through minefields. They were used as cannon fodder. They would be sent out in front of patrols to try and draw the enemy fire. That’s what Russia is doing with these people. And they’re all young. Putin is throwing away a generation of his youth in the Ukraine for nothing.”

Whelan, a former US Marine, was released earlier this year as part of a sweeping prisoner exchange carried out between the United States and Russia. A total of eight people were returned to the Kremlin in exchange for the release of 16 people who were held in Russian detention, including four Americans, in the historic swap that was the result of years of complicated behind-the-scenes negotiations involving the US, Russia and Germany.

CNN’s Jennifer Hansler contributed to this report.