Four actors in an anti-war multimedia drama have been arrested at Belfast City airport for possessing live rounds of ammunition.

The four almost unwittingly brought 12 live bullets on to a plane as they began their return journey to Sarajevo after staging The Conquest of Happiness during Derry's UK City of Culture celebrations.

The Guardian has learned that the four were detained at the George Best Belfast City airport on Monday evening after the bullets, which were sewn into the lining of a jacket worn by one of the actors on set, were discovered by a scanner.

A spokeswoman for Belfast's Prime Cut Productions and Sarajevo's East West Centre – the theatrical companies behind the project – said the actors and production staff were totally unaware that the ammunition was in the lining of the denim jacket.

"The jacket was bought on a shopping website and so presumably that is where the bullets came from, but the actors had no idea the bullets were there," she told the Guardian.

The four were arrested and held until 4.30pm at Musgrave Street police station in central Belfast and then released without charge. They included Belfast-based Emma Jordan from Prime Cut productions.

They were said to be shaken by the ordeal, and the irony of being arrested for possessing ammunition while touring with an anti-war show was not lost on them.

The joint Irish-Bosnian group is now travelling to Sarajevo to join the production for its presentation at the Mess international festival in Mostar on Friday night, where it will be performed on the Unesco world heritage site of the Old Bridge, which was blown up during the Bosnian war and rebuilt in 2004.

The Conquest of Happiness, which explores and re-enacts scenes from some of the worst atrocities of the 20th and 21st centuries and includes a scene from Bloody Sunday, is directed by world renowned peace activist Haris Pasovic and has received rave reviews since its premiere in Derry last week.

Pasovic, who also wrote The Conquest of Happiness, told the Guardian prior to the production in Derry that the last thing Northern Ireland needed was "the human rights industry" to cope with its violent past.

Speaking in Belfast, Pasovic called for artists to become more involved in post-conflict situations in Bosnia and Northern Ireland.

The Bosnian director kept producing plays – including a version of Samuel Beckett's Waiting for Godot with Susan Sontag – even while Serbian shells, mortars and machine guns rained down on Sarajevo during the siege in the early 1990s.