Five American prisoners were released from Iranian custody on Monday after the U.S. agreed to return $6 billion of Iranian oil revenue that was frozen under American sanctions, according to media reports.

The Biden administration also released five convicted Iranian nationals as part of the deal.

“Siamak Namazi, Morad Tahbaz, Emad Sharghi, and two citizens who wish to remain private will soon be reunited with their loved ones — after enduring years of agony, uncertainty, and suffering,” President Joe Biden said in an official White Hosue statement without mentioning the $6 billion or the release of the Iranian nationals. “I am grateful to our partners at home and abroad for their tireless efforts to help us achieve this outcome, including the Governments of Qatar, Oman, Switzerland, and South Korea.”

Iran previously owned the oil revenues before they were frozen in a South Korea bank, which transferred the funds to accounts in Qatar. U.S. officials say the money will be monitored to ensure Iran uses it for humanitarian needs such as food, agricultural products, and medicine, which are not subject to U.S. sanctions.

However, some Republicans aren’t buying it.

Senator Tom Cotton (R., Ark.) accused Biden of paying a ransom, saying the agreement is a “craven act of appeasement.”

Former secretary of state Mike Pompeo posted a similar statement on X, formerly known as Twitter. While he’s glad the American hostages are returning to the U.S., he said, he fears the deal will only encourage Iran to imprison more Americans.

Pompeo also drew attention to Iran’s announcement of a new drone that could threaten Israel while noting the timing of the news.

The White House denied paying a ransom. John Kirby, a spokesman for the National Security Council, argued that because Iran previously owned the oil revenues that were frozen, it’s not considered a ransom.

The five American prisoners landed in Qatar on Monday before flying to the U.S.