Thousands of people took to the streets of Brussels on Sunday to protest against the detention in Iran of Belgian aid worker Olivier Vandecasteele.

He was arrested last year and recently sentenced to a minimum 28 years in prison on charges including spying.

The Belgian government has said the charges are fake.

"His life is in danger, contribute to his freedom," "#Free Olivier Vandecasteele," read banners held by protesters who included Vandecasteele's family, friends and colleagues.

After Vandecasteele was sentenced last month, Belgium's justice minister said the Belgian had been imprisoned "for a fabricated series of crimes" and had been sentenced as retribution for a 20-year jail term Belgian courts imposed on an Iranian diplomat in 2021.

Belgium's constitutional court will next month hold a hearing on the legality of a Belgian prisoner exchange treaty with Iran. Belgian media has suggested this could lead to a prisoner swap between the two countries involving the Iranian diplomat, convicted of planning a bomb plot against an exiled opposition group, and Vandecasteele.

Opponents of the deal say that the deal would provide Iranian spies and potential terrorists de facto immunity in Belgium, turning the country into a base for dangerous activities.

Iran routinely detains Western citizens on bogus charges using them as bargaining chips to achieve its goals in disputes with the West.

With reporting by Reuters