Belgium and Iran conducted a prisoner exchange Friday in Oman, with officials saying Tehran released a Belgian aid worker in exchange for an Iranian diplomat convicted of attempting to bomb a meeting of exiles in France.
The initial announcement by Oman's Foreign Ministry did not identify the prisoners being swapped.
Later Friday, Belgian Prime Minister Alexander De Croo said in a statement that the aid worker, Olivier Vandecasteele, had been freed. Iranian state television later confirmed that the diplomat, Assadollah Assadi, was freed as well.
Oman's Foreign Ministry said that "those released were transferred from Tehran and Brussels to Muscat today, Friday, in preparation for their return to their countries." It added that "the sultanate of Oman appreciated the high positive spirit that prevailed in the talks in Muscat between the Iranian and Belgian sides, and their keenness to settle this humanitarian issue."
De Croo said Vandecasteele was transferred to Oman on Thursday night. He was received by a team of Belgian diplomats and military officials, then was assessed by doctors.
"Olivier spent 455 days in prison in Tehran. In unbearable conditions. Innocent," De Croo wrote. "Olivier Vandecasteele's return to Belgium is a relief. A relief for his family, friends and colleagues."
Oman has long served as an interlocutor for the West with Iran.
In January, Iran sentenced Vandecasteele to a lengthy prison term and 74 lashes after convicting him of espionage in a closed-door trial. He also was fined $1 million. Vandecasteele was arrested in Iran in February 2022 while packing up his belongings, after working with the Norwegian Refugee Council and Relief International in the Islamic Republic from 2015 to 2021, according to Amnesty International.
His family and the Belgian government strongly denied Iran's claims, made without offering evidence, that he was a spy. To make the swap with the Iran diplomat possible, Belgium had adopted in March a controversial prisoner exchange treaty that was upheld by the country's constitutional court.
In 2021, Belgium convicted Assadi of masterminding a thwarted bomb attack against an exiled Iranian opposition group in France and sentenced him to 20 years in prison. Prosecutors tied Assadi to a couple, stopped by the Belgian police and found with 550 grams (1.21 pounds) of TATP explosives and a detonator in 2018. They had been trying to target a meeting in Villepinte, France, of the Mujahedeen-e-Khalq, an exiled Iranian opposition group known as the MEK.
Among dozens of prominent guests at the rally in Villepinte that day were then-President Donald Trump's lawyer, Rudy Giuliani; Newt Gingrich, former conservative speaker of the U.S. House of Representatives; and former Colombian presidential candidate Ingrid Betancourt.
Assadi was arrested a day later in Germany and transferred to Belgium. Belgian intelligence identified him as an officer of Iran's intelligence and security ministry who operated undercover at the Iranian Embassy in Austria. Iran denied Assadi's involvement.
Iran has carried out kidnappings and other plots against dissidents abroad in the past. However, Iranian Foreign Minister Hossein Amirabdollahian referred to Assadi as "an innocent diplomat" in a tweet after his release on Friday. Iranian state television called the case against him "bogus accusations."
In a statement, the MEK condemned Assadi's release, calling it "a shameful ransom to terrorism and hostage-taking."
"This will embolden the religious fascism ruling Iran to continue its crimes in Iran through repression and regional and international terrorism," the group said.
Iran has detained a number of foreigners and dual nationals over the years, accusing them of espionage or other state security offenses and sentencing them following secretive trials in which rights groups say they have been denied due process.
Critics have repeatedly accused Iran of using such prisoners as bargaining chips with the West.
Iran, facing Western sanctions over its rapidly advancing nuclear program, has faced protests in recent months and economic strain. Oman's Sultan Haitham bin Tariq was already scheduled to visit Tehran this weekend before the announced prisoner swap.