Erdogan warned protesters to cheers from the crowd: "I say this very clearly: either Taksim Square is cleared, or the security forces of this country will know how to clear it."
A violent police crackdown on what began as an environmental protest over a redevelopment plan at the park has sparked a much broader expression of discontent about Erdogan's government, and what many say is his increasingly authoritarian decision-making.
The anger has been fanned because riot police have at times used tear gas, water cannons, and rubber bullets to disperse mostly peaceful protesters. Five people, including a police officer, have died and thousands of people have been injured, denting Erdogan's international reputation.
Erdogan, who was elected with 50 percent of the vote for his third term in 2011, vehemently rejects the accusations by protesters and points to his strong support base.
A second pro-government rally is planned for Sunday in Istanbul, though Erdogan has previously said that the rallies were not designed as "an alternative" to the demonstrations at Gezi Park, but part of early campaigning for local elections next March.
On Saturday, Erdogan lashed out at what he called the "plot" behind the biggest street protests in his 10-year tenure.
"Over the last 17 days, I know that in all corners of Turkey, millions and billions have prayed for us," Erdogan said, as he moved about the stage. "You saw the plot that was being carried out, the trap being set." He said his supporters represented the "silent masses."
"You are here, and you are spoiling the treacherous plot, the treacherous attack!" he said, insisting unspecified groups both inside and outside Turkey had conspired to mount the protests centered on Istanbul — and that he had the documents to prove it.
The crowd chanted in response: "Stand straight, don't bow, the people are with you!"
In his speech, he focused on some protesters who have clashed with polices — at time by throwing stones and firebombs.