A district court in The Hague has convicted a pro-Syrian regime militia fighter of war crimes and crimes against humanity for complicity in torture and illegal arrest in Syria and sentenced him to 12 years in prison.

Judges ruled on Monday that the 35-year-old man, identified in court only as Mustafa A, was involved in the arrest of a man in 2012 in Syria.

He later handed the man over to Syrian Air Force intelligence officials who ran a prison where he was tortured.

The court said A was a leading member of the Liwa al Quds, or the Jerusalem Brigade. Liwa al Quds is a militia made up mostly of Palestinian refugees living in Syria founded during the early years of Syria's 12-year civil war.

He was convicted of war crimes and crimes against humanity for complicity in torture, inhumane treatment and illegal arrest and also for membership of a criminal organisation.

The judgment marks the first time a Dutch court has convicted someone for crimes committed while fighting on the side of regime leader Bashar al Assad during the war in Syria.

There have been a handful of similar convictions in Germany.