ISTANBUL—Violence between protesters and police erupted and spread for a second consecutive day in Istanbul on Sunday, as Prime Minister Recep Tayyip Erdogan sought to regain the political agenda by staging a massive rally, after ejecting protesters from their park encampment the previous day.

Meanwhile, there was renewed fighting in Ankara and five unions called a general strike for Monday. There was also some violence between supporters and opponents of the government.

The second straight day of clashes flared through pockets of Istanbul as the government widened a crackdown it launched against protesters late Saturday, when it cleared a protester encampment from Gezi Park, the symbolic heart of demonstrations entering their 18th day.

A short distance away, Mr. Erdogan on Sunday took the stage to address a rally estimated at under 300,000 supporters of the governing Justice and Development Party, or AKP, and declared victory over the protests in the biggest show of political force since the protests began. The premier chided the protesters for rejecting an offer he had made to mollify them.

Five people have been left dead from 18 days of protests and more than 5,000 injured.