"They do not like Americans and they don't try to hide that," Reed, 30, told ABC News in an interview airing Friday on "Good Morning America."
The U.S. Marine veteran was imprisoned in Russia for nearly three years. Reed, a Texas native, was arrested in Moscow in the summer of 2019 while visiting his Russian girlfriend. Russian authorities accused him of assaulting officers while being driven to a police station after a night of heavy drinking. He was convicted by a Russian court in mid-2020 and sentenced to nine years in a prison camp.
"There's pretty horrible conditions there," Reed said. "Some of those places don't have a toilet -- there's just a hole in the floor for where the toilet should be."
"There's rats, [the] food there could be, you know, really bad," he added. "In the summer, it's very hot there. There's no air conditioning obviously, or even fans inside of those cells."
Reed was ultimately freed on April 27 as part of a prisoner swap agreed between the United States and Russia.
"The real fear that you have that just kind of sits on you like this weight the whole time, is that, you know, you could be there forever," he said.
Griner, who plays professional basketball for the Phoenix Mercury, was returning to Russia to play in the off-season when she was detained at Sheremetyevo International Airport near Moscow on Feb. 17, after being accused of having vape cartridges containing hashish oil, which is illegal in the country. On Thursday, the two-time Olympic gold medalist pleaded guilty to drug possession charges on the second day of her trial in a Russian court.
Griner, 31, also told the court that she had no "intention" of breaking Russian law, adding that she was in a rush when packing and did not mean to leave the cartridges in her bag. The trial was then adjourned until July 14.
Her detention has been extended repeatedly, most recently through Dec. 20, which was the expected length of her trial. If convicted, Griner faces up to 10 years in Russian prison and also has a right to an appeal.
The U.S. government has classified Griner's case as "wrongfully detained," meaning Washington will more aggressively work to negotiate her release even as the legal case against her plays out, according to the U.S. Department of State.
The White House said in a statement Wednesday that President Joe Biden and Vice President Kamala Harris have called Griner's wife, Cherelle Griner, to discuss efforts to release her.
Griner had personally reached out to Biden in a handwritten letter that the White House received on Monday, when Americans were celebrating Independence Day. In the letter, she urged Biden to help her and other American detainees get out of Russia.
"As I sit here in a Russian prison, alone with my thoughts and without the protection of my wife, family, friends, Olympic jersey or any accomplishments, I'm terrified I might be here forever," Griner wrote to the president. "It hurts thinking about how I usually celebrate [the Fourth of July] because freedom means something completely different to me this year."
Paul Whelan, a former U.S. Marine and Michigan-based corporate security executive, has been detained in Russia since his December 2018 arrest on espionage charges, which both he and the U.S. government claim are false. Whelan, 52, was left out of the April prisoner exchange that led to Reed's release.
Reed said the Biden administration is "not doing enough" to free Griner and Whelan.
"I hope that President Biden and his administration will do everything possible to get both, you know, Brittney and Paul out of Russia, and that they will do that immediately," he told ABC News. "Because every day that, you know, they sit here and wait to make a decision is one more day that, you know, Paul and Brittney are suffering."
Reed noted that freeing Whelan "needs to be the no. 1 priority there, just simply based off of the fact that he's been there the longest." He also criticized the Biden administration for contacting Griner's family but not Whelan's.
"They called Brittney's family, and I'm extremely excited that they did that. I think that's a step in the right direction," Reed said. "But, at the same time, they did not contact Paul Whelan's family and he's been there for longer than I was even in Russia."
During a news briefing Thursday, White House press secretary Karine Jean-Pierre declined to say whether Biden has plans to call Whelan's family, telling reporters that she didn't have a telephone call to "announce or preview." But she described regular contact between the Biden administration and the Whelans.
"The president is getting regularly updated," Jean-Pierre told reporters. "This is top of mind."
She added: "We're going to do everything that we can to bring home Brittney Griner safely, and to also make sure that we bring Paul Whelan back home as well."