Supporters of Turkey's opposition began a 400-kilometre Ankara-to-Istanbul march Thursday to protest a 25-year jail sentence handed down a day earlier to a lawmaker found guilty of leaking government information.
Kemal Kilicdaroglu, chief of the centre-left Republican People's Party (CHP), was surrounded by supporters holding up signs saying "justice" as they began the long walk.
"We do not want to live in a country without justice," Kilicdaroglu said.
On Wednesday, a court handed down the lengthy prison sentence to Enis Berberoglu, a CHP member of parliament who was found guilty of leaking information showing that Turkey was sending weapons to Syrian rebels.
Prosecutors said Berberoglu gave the information - showing a truck belonging to the intelligence service shipping weapons and ammunition in 2014 - to the newspaper Cumhuriyet, which published a story in 2015.
Cumhuriyet itself has been under intense pressure - more than a dozen of its journalists and executives have been in jail for more than six months awaiting trial - while former editor-in-chief Can Dundar, the main reporter on the weapons report story, lives in exile in Europe.
Jailing of opposition members has focused recently on the pro-Kurdish Peoples' Democratic Party (HDP), which has 11 legislators behind bars. Thousands of HDP members are also jailed, allegedly for links to terrorism.
Berberoglu is the first major CHP figure to be arrested under the ongoing crackdown in the country.
Secular opposition groups in Turkey have been sceptical of the government's support for Syrian rebel groups, amid concerns about the rise of violent Islamism.
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