An appeals court on Thursday increased the prison sentences of four Islamic radicals accused of plotting attacks on Dutch politicians, convicting them of the additional charge of membership in a terrorist organization.

The Hague appeals court re-convicted the four Dutch nationals of Moroccan descent for plotting attacks, and said trial evidence showed they were part of a single group, as prosecutors had argued.

Judges cited their adherence to a single violent belief system, their training with firearms, and their coordinated efforts to find the addresses of Dutch politicians on a hit-list, including the prime minister.

The court's judges added a year to the sentence of ringleader Samir Azzouz, 22, giving him a total of nine years in prison. Azzouz had videotaped a suicide testament.

Both defendants and prosecutors had appealed the original ruling. The defendants asked for acquittal and the prosecutors sought longer sentences, including 15 years for Azzouz.

Azzouz "has made it apparent that he despises Dutch society," judges said in a written ruling. "He has shown that he has no respect for those who have different views and knows no compassion for the potential victims of the acts he planned."

Azzouz evaded jail twice in investigations into alleged terrorist activities. The first time, he was caught with bomb-making materials, but he was released without charge on a technicality.

He later was charged with planning an attack, but was acquitted when the judges ruled his preparations were not advanced enough to prove a terrorist intent.