The men, who were not identified, had all been contacted via social networks to inform them of their court dates and the charges, as the Netherlands seeks to get tough on Dutch citizens who have joined jihadist groups.

"It was found that these three men travelled to the conflict zone in Syria and in Iraq and joined a terrorist organisation," the court said in a statement.

Two of them were sentenced to six years in prison, and a third who was "seen on the internet in a propaganda file for Islamic State" was given seven years for being a "figurehead for this terrorist organisation's armed fight."

"Even though the suspects did not appear before the hearing" the court "concluded that they were aware that it was being held," the statement added.

The Rotterdam court will also rule in the cases of seven other suspected jihadist fighters on Thursday who also remain at large.

At least 280 people have left the Netherlands since the start of Syria's civil war in 2011 to join jihadist groups, with about 185 still believed to be in the region. From available official figures, it is thought 45 have returned while another 45 were killed in the fighting.