Turkish security forces detained the 30-year-old man and 24-year-old woman -- Miroslav Farkas and Marketa Vselichova -- in Turkey's southeastern Sirnak province that borders Syria and Iraq on November 13, 2016.

Turkish prosecutors said that material was found on their phones showing photos with the YPG, sound files and YPG marching music.

The two were charged with "membership of an armed terror group" and prosecutors had asked for up to 15 years in jail.

The Czech denied the charges, insisting they were humanitarian aid workers.

But a Turkish court sentenced both to six years and three months behind bars on Wednesday, the Czech foreign ministry said.

Czech Foreign Minister Lubomir Zaoralek called the verdict a "huge disappointment" and also insisted in a Wednesday statement that it must be appealed.

The YPG is seen by Turkey as the Syrian arm of the outlawed Kurdistan Workers Party (PKK) which has waged an over three decade insurgency against the Turkish state.

But the United States works closely with the group as the best ground force in Syria to defeat Islamic State (IS) jihadists. Turkey's NATO allies do not regard the YPG as a terror organisation.

Wednesday's sentencing comes as tension is rising between Turkey and the European Union over the scale of Ankara's crackdown in the wake of last year's failed coup.

Turkish authorities also arrested a British citizen on Saturday while he was holidaying on the country's western coast on charges of working with the YPG.

The man, named as Joseph A.R., was detained in the Aegean holiday resort town of Didim in Aydin province and then remanded in custody by a court ahead of trial.