Mr. Berberoglu has become one of about 50,000 Turks arrested since the introduction of a state of emergency last summer which was initially intended to target the plotters of a failed coup in July, but which has since been used to crack down on most forms of opposition. More than 140,000 people have been fired or suspended from their jobs.

Other notable cases in recent days include the arrest of Taner Kilic, the chairman of the Turkish branch of Amnesty International, and the sentencing of Aydin Sefa Akay, a judge who was a member of a United Nations war crimes panel. Judge Akay was sentenced to more than seven years in prison on charges of belonging to the Gulen movement, the group accused of being behind the failed coup.

Judge Akay’s jailing was condemned on Thursday by Judge Theodor Meron, the president of the Mechanism for International Criminal Tribunals, which is overseen by the United Nations. Judge Meron, who has referred the matter to the United Nations Security Council, said the Turkish government “has pursued domestic proceedings in disregard of the applicable international legal framework.”

Mr. Kilicdaroglu said at the beginning of his walk on Thursday that he was marching in support of those who had been unjustly included in the purge.