A US citizen held since June is among dozens released in a prisoner swap between Ukraine and Russia.
Ukrainian President Volodymr Zelensky said in his nightly address Ukraine had received 64 soldiers, including four officers and 60 other troops.
In a tweet, a top adviser to Mr Zelensky said the deal also freed an American, Suedi Murekezi.
A White House spokesman refused to confirm the deal, but told reporters: “We certainly welcome that news.”
Ukrainian chief of staff Andriy Yermak said the military personnel released had fought in Donetsk and Luhansk.
In a post on social media he said Mr Murekezi – a US Air Force veteran – had been helping the Ukrainian people before he ended up in Russian custody.
Russia’s Tass news agency has reported that Mr Murekezi was arrested in the eastern Donetsk region in June.
He was charged with attending anti-Russian protests and inciting ethnic hatred.
Mr Suedi told ABC News he had spent weeks in a “torture chamber” of a basement, where he was subjected to electric shocks and beaten by captors.
He said the Russians had accused him of being a CIA operative.
The Rwandan-born crypto investor settled in Ukraine in 2018, according to the Washington Post.
He reportedly lived in the US state of Minnesota and spent eight years in the US Air Force until 2017.
White House National Security Council spokesman John Kirby said he could not confirm Mr Murekezi’s release due to privacy considerations.
Mr Murekezi was held for a time with two other Americans who had travelled to Ukraine to fight.
Alexander John-Robert Drueke and Andy Tai Ngoc Huynh were freed by Russia in September in a Ukraine-Russia prisoner swap brokered by Saudi Arabia.