Shops and banks closed early on Wednesday as the West African nation braced for fresh protests over a court case that has fuelled tension and violence ahead of presidential elections next year.
Violence broke out on the day of Sonko's last court appearance on March 16, as police fired tear gas at supporters accompanying his motorcade to the courthouse.
Sonko has called for more nationwide protests on Wednesday, Thursday and April 3.
Police fired several rounds of tear gas and stun grenades forcing mostly student protesters to retreat into the campus from where they hurled rocks.
He is also on trial for allegedly raping a beauty salon employee in 2021 and making death threats against her.