Selek, 43, known for her critical studies of the Kurdish conflict in Turkey and work with street children, lives in exile in France and did not attend the hearing at the Supreme Court of Appeals.

Last year, another Turkish court sentenced her to life in prison for "terrorism" and found the academic guilty of helping Kurdish rebels carry out an attack 16 years ago on an Istanbul spice market popular with tourists.

Selek, who was granted political asylum by France, was arrested and jailed aged 27 on charges of involvement in the explosion after she refused to give police the names of rebels she had met during her research.

She was freed in 2000 after the publication of a report blaming the explosion on a gas leak.

Turkish courts acquitted her three times of involvement, basing their decisions on the primary witness's retraction of his testimony and a lack of evidence that the blast was a bomb attack.

But the high court of appeal threw out the verdict each time.

After Wednesday's ruling, a retrial is expected to begin from scratch in Istanbul, again in Selek's absence.