The leader of the main opposition party in Turkey is set to complete the final stretch of a 25-day "March for Justice" from the capital Ankara to Istanbul.

Republican People's Party leader Kemal Kilicdaroglu launched the 425-kilometer (265 miles) march after a parliamentarian was imprisoned in June, but the outcry has since grown to protest the massive crackdown that began after last summer's failed coup attempt.

Tens of thousands of people have joined Kilicdaroglu on his march in scorching heat, chanting "rights, law, justice." Kilicdaroglu will walk the final leg alone and end the march Sunday with a mass rally in Istanbul.

Istanbul governor Vasip Sahin said 15,000 police officers have been dispatched for security. The U.S. Consulate issued a security message asking American citizens to exercise caution.