"I believe that this case is completely irrelevant in legal terms, because nothing imputable [against them] exists," Erlantz Ibarrondo, the lawyer of Hector Arroyo, one of those arrested, told Sputnik.
The trial is to take place Thursday, Ibarrondo said, adding that his client was feeling "well" and "calm."
According to official information, the arrested men travelled to Ukraine in 2014 and later returned to Spain. An Interior Ministry spokesman stated that all the detainees were fighting "on the same side", however he could neither confirm nor specify whether they fought alongside Kiev forces or independence supporters.
Following the arrest, Agustin Rivas, a representative of the Madrid Committee in Support of Anti-Fascist Ukraine, told Sputnik that those arrested were fighting for the Donbas militias.
The conflict in Ukraine began in April 2014, when Kiev launched a military operation against independence supporters in the country's southeast.