ISTANBUL -— Riot police reinforcements arrived in Istanbul on Sunday morning to help quell demonstrations across the city, as protesters remained defiant a day after police evicted activists from Gezi Park.

Bulldozers cleared the tent city and barricades set up by protesters on Taksim Square while police sealed off the area to keep demonstrators away from the spot that has become the focus of the strongest challenge to Prime Minister Recep Tayyip Erdogan in his 10 years in office.

Amnesty International reported four people have died and thousands have been injured since the unrest began May 31 when riot police attempted to remove protesters from Gezi Park, which is slated for demolition. The Turkish Medical Association puts the number of injured at 7,500.

Taksim Solidarity — an umbrella group that helped organize the mass demonstrations against the government — has called on supporters to gather in Istanbul's Taksim Square.

Crowds amassed Sunday along several arteries leading to the square but are being held back by riot police firing tear gas and water cannon, witnesses told USA TODAY.

Meanwhile, senior figures in Erdogan's ruling Justice and Development Party have warned that anyone who defies a ban on the demonstrations would be considered a terrorist and treated accordingly.

"From now on the state will unfortunately have to consider everyone who remains there a supporter or member of a terror organization," Minister for European Union Affairs Egemen Bagis said late Saturday. "The protests from now on will play into the hands of some separatist organizations that want to break the peace and prioritize vandalism and terrorism."

Many demonstrators on the ground reject being labeled as extremists. Baris Uyar, 35, an electronic engineer, said he'd been demonstrating for more than two weeks.

"I don't know, of 10,000 people, there might be one person throwing a stone, but the police were throwing tear gas at those thousands of people," he said. "There is provocation on several sides, but the main duty of a democratic government is to prevent such things."

Amnesty said police detained more than 100 people overnight Saturday but refused to release information on their identities or whereabouts.

"Following a night of shocking police violence, the authorities are now denying due process to those they have detained," Andrew Gardner, Amnesty International's researcher in Istanbul, told reporters. "The police must release them immediately or disclose their location and allow access to family members and lawyers."

The London-based human rights group criticized police tactics of using tear gas and water cannon laced with a chemical irritant on thousands of demonstrators trying to reach Taksim Square.

"Protests have been overwhelmingly peaceful, and there is no legitimate reason to prevent all forms of protest in the area," Gardner said.

Erdogan is scheduled to address his supporters at a rally in the western part of the city on Sunday. Thousands are expected to attend the rally, which follows a similar event Saturday in the capital of Ankara, where the prime minister said his party spoke for a silent majority.

"The people of Turkey protect their government," he said Saturday. "The people of Turkey protect their democracy and willpower."