May 23 (UPI) — A prisoner swap is underway Friday between Ukraine and Russia, Ukrainian officials said.

The swap, involving 1,000 prisoners from each side, began on Friday and was not yet completed, Radio Free Europe/Radio Liberty, The Kyiv Independent and CNN reported.

The process of exchanging the prisoners is expected to take several days, CNN reported.

U.S. President Donald Trump, however posted on his Truth Social account Friday that the swap had been completed.

“A major prisoners swap was just completed between Russia and Ukraine. It will go into effect shortly,” Trump said. “Congratulations to both sides on this negotiation. This could lead to something big?”

A source familiar with the matter, however, told The Kyiv Independent the swap was still ongoing.

Ukrainian President Volodymyr Zelensky posted to social media Thursday that the prisoner swap “was perhaps the only tangible result of the meeting in Turkey.”

“We are working to ensure that this result is achieved,” he wrote.

The two sides met last week in Istanbul and Zelensky continued that Ukraine’s Minister of Defense Rustem Umerov is involved with the “organization of the process and the implementation of the agreement,” but several other prominent members of the Ukrainian government have also taken part in the process.

Zelensky also added that his team is “clarifying the details for each individual included on the lists submitted by the Russian side.

“Returning all of our people from Russian captivity is one of Ukraine’s key objectives,” he said.

He also posted Monday that “the most significant outcome of the meetings [in Turkey] was the agreement to conduct a prisoner exchange in a 1,000-for-1,000 format.”

Additionally, Ukraine’s Coordination Headquarters for the Treatment of Prisoners of War had announced on Telegram last week that Russia had returned the bodies of 909 Ukrainian soldiers.