Turkish riot police fired tear gas and water cannons today at demonstrator trying to return to Istanbul's main square, maintaining a hard line against rekindled protests as the prime minister's supporters prepared to rally across town.

Police in uniform and plainclothes sealed off Taksim Square and adjacent Gezi Park, which riot police cleared yesterday evening. Crews worked through the night to remove all traces of a sit-in that started more than two weeks ago and became the focus of the strongest challenge to Prime Minister Recep Tayyip Erdogan in his 10 years in office.

Istanbul's governor, Huseyin Avni Mutlu, said the square was off-limits to the public for the time being, and nobody would be allowed to gather. A spokesman for the protesters vowed the group would retake Gezi Park.

"We will win Taksim Square again and we will win Taksim Gezi Park again," Alican Elagoz said.

A call went out for another demonstration in Taksim Square for today afternoon, but the area was within a tight police cordon, with passers-by subjected to identity checks and bag searches. Thousands of protesters trying to reach the area were stuck on side streets in a blanket of tear gas.

Erdogan, who has repeatedly insisted that the protests were part of a nebulous plot by bankers and foreign media to destabilize Turkey, was to deliver a speech at a political rally in an area of Istanbul about 10 kilometers (6 miles) from the square.

A similar speech in Ankara yesterday before the raid was attended by tens of thousands of supporters, who cheered him as he warned protesters that security forces "know how to clear" the area.

The protests began as an environmental sit-in to prevent a development project at Gezi Park, but anger over a violent crackdown there quickly spread to dozens of cities and spiraled into a broader expression of discontent with what many say is Erdogan's increasingly authoritarian decision-making.

He vehemently denies the charge, pointing to the strong support base that helped him win a third consecutive term with 50 percent of the vote in 2011. The protests have left at least five people dead, including a police officer, according to a Turkish rights group, and more than 5,000 injured, denting Erdogan's international reputation.

In clashes that lasted through the night and into the morning in Istanbul, Turkey's largest city, protesters set up barricades and plumes of tear gas rose in the streets.

Television footage showed police detaining medical personnel who had been helping treat injured protesters, leading them away with their hands cuffed behind their backs.

Riot police also entered a shopping mall in an upscale neighborhood of central Istanbul, apparently searching for protesters.

In Ankara, the capital, police ratcheted up the pressure in the early afternoon, firing water cannon, rubber bullets and tear gas at central Kizilay Square. At least four people were injured. Earlier, police had dispersed hundreds who tried to hold a memorial service for a protester who died of injuries sustained in a nearby police crackdown on June 1.