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Three Dutch men were sentenced to up to seven years in jail for joining a "terrorist" organisation in Iraq and Syria.

The trio, who were not identified, were sentenced in absentia by a Rotterdam court on Tuesday, which contacted them using social media.

The men 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.

Earlier this month, two suspected jihadist fighters were detained by Dutch authorities after they returned from Turkey where they had been sentenced for terror-related activities, prosecutors said.

The two Dutch nationals, identified by local media as Reda Nidalha and Oussama H. "were detained upon their arrival at Schiphol airport," the public prosecution service said in a statement.

A Turkish court sentenced the men to six years behind bars in May following their arrests in 2016, after they came across the Syrian border back to Turkey.

The men, both 23, allegedly joined the Islamic State Group in 2014, but later decided they wanted to go back to the Netherlands.

"They were on their way to a Dutch diplomatic post when they were arrested by Turkish authorities," the NOS public newscaster said.

The men are appealing the sentence and were out on bail. They were given permission to travel to the Netherlands while awaiting the outcome of their appeal in Turkey, but at the same time they will also be put on trial by a local court, prosecutors said.

Meanwhile the Dutch government also asked Kurdish authorities Tuesday to hand over three women who are currently being held in camps in northern Syria.