CHP leader Kilicdaroglu called the march after CHP lawmaker Enis Berberoglu was sentenced to 25 years in jail on Wednesday
Turkish President Recep Tayyip Erdogan on Saturday warned the leader of the main opposition party against making a planned protest march from Ankara to Istanbul, telling him "don't be surprised" if legal proceedings were opened.
Republican People's Party (CHP) leader Kemal Kilicdaroglu called the march after former journalist turned CHP lawmaker Enis Berberoglu was sentenced to 25 years in jail on Wednesday for leaking classified information to a newspaper.
Kilicdaroglu is now on the third day of a trek that is expected to take almost a month and represents by far his biggest challenge to the Turkish strongman since he took over the CHP in 2010.
But Erdogan said his actions were damaging for the country and appeared to warn Kilicdaroglu he could even face legal troubles.
"Calling people out onto the street is neither good for them or for the country," Erdogan told a business conference in Istanbul.
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"Wandering around with a 'justice' placard in your hand is not going to bring justice. If you are looking for justice, then the place in Turkey to find justice is the parliament."
He added: "If the judicial authorities invite you in somewhere tomorrow then don't be surprised."
Kilicdaroglu, 68, has made the word "justice" the slogan of his march, clutching a stick with the word emblazoned on a card.
His plan is for the 450-kilometre (280 miles) trek to culminate at Maltepe prison in Istanbul where Berberoglu is being held.
Political tensions have been rising in Turkey after Erdogan on 16 April narrowly won a referendum granting him greater powers that the CHP fears will lead to one-man rule.
Kilicdaroglu in an interview with AFP on Friday accused Erdogan of staging a "second coup" with the crackdown that followed last July's failed putsch.
A dozen MPs from the pro-Kurdish Peoples' Democratic Party (HDP) had already been arrested under the emergency declared after the coup bid.
But Berberoglu's arrest was the first time an MP from the CHP, the main secular opposition founded by first president Mustafa Kemal Ataturk, has been held.