An Iranian diplomat has been convicted of planning a foiled attack on Tehran opponents in France in 2018.
Assadollah Assadi was found guilty by a Belgian court of "attempted murder of a terrorist nature" and "participation in the activities of a terrorist group".
The court in Antwerp imposed the maximum 20-year prison term, as requested by prosecutors. Assadi had denied the charges and was absent for the judgment.
Three Belgian accomplices of Iranian origin were also sentenced to between 15 to 18 years in prison, as well as forfeiture of their Belgian nationality.
The case has heightened diplomatic tensions between Tehran and several European countries, including France.
The Iranian regime had stated before the trial that legal proceedings were "not legitimate" because Assadollah Assadi had claimed diplomatic immunity.
During the trial, lawyers for the intended targets of the attack claimed without offering evidence that the diplomat had been working on direct orders from Iran's highest authorities. Tehran has denied the allegations.
But in its ruling, the Belgian court found that the four suspects were members of a cell operating for Iran's intelligence services, and had been gathering information to identify opponents for an attack.
The intended target for the bombing was a large annual gathering of the National Council of Resistance of Iran (NCRI), which included members of the People's Mojahedin Organization of Iran (MEK).
On 30 June 2018, Belgian police officers were warned about a possible bomb attack at the annual meeting of the MEK at an exhibition complex in the French town of Villepinte.
On the same day, a Belgian-Iranian couple living in Antwerp was arrested near Brussels, traveling with over 500 grams of TATP explosive and a detonator in their car.
Belgium's bomb disposal unit said the device was professionally made and could have caused a sizable explosion at the event north of Paris.
Among 25,000 guests at the rally were Newt Gingrich, former conservative speaker of the U.S. House of Representatives; and former Colombian presidential candidate Ingrid Betancourt.
Assadi, a Vienna-based diplomat was detained the next day in Germany and transferred to Belgium. The court said that the official was on vacation at the time of his arrest and was not entitled to immunity.
Prosecutors said he was the "operational commander" of the planned attack and had brought the explosives to Austria on a commercial flight from Iran and delivering them to the couple in Luxembourg.
Nasimeh Naami was identified as having a "manipulative" personality and was sentenced to 18 years in prison, and her partner Amir Saadouni to 15 years.
The fourth defendant, a dissident poet, was presented by prosecutors as an Iranian intelligence agent acting from Belgium and received a 17-year prison sentence.
The leader of the MEK, Maryam Rajavi, welcomed the court's ruling and denounced the planned attack as "state terrorism".
"The time has come for the European Union to take action," Rajavi said, urging EU countries to recall their ambassadors from Tehran following the ruling.
The NCRI was founded in the 1960s and claims to be the most important and most structured opposition movement among exiled Iranian opposition groups.
Until several years ago, it had been classified as a terrorist organisation by the EU and United States but was removed from the list after denouncing violence.