A man shouts as plain clothes security members try to detain a person who was reading as security close the city's landmark Taksim Square and Gezi Park on the first anniversary of last year's protests in Istanbul, Turkey, Saturday, May 31, 2014. A government backed redevelopment plan for Gezi Park in Istanbul sparked anger and morphed into nationwide anti-government protests in June, leaving eight people dead and thousands other injured.(AP Photo/Emrah Gurel)

ISTANBUL - Hundreds of activists mobilized Saturday for demonstrations in Istanbul and other cities, defying a heavy police presence on the anniversary of nationwide anti-government protests that erupted last year.

Police blocked access to Istanbul's main square, Taksim, and news reports said some 25,000 police officers and up to 50 anti-riot water cannon vehicles would be deployed around the city. Prime Minister Recep Tayyip Erdogan warned activists to keep away from the square, saying authorities were under strict orders to prevent protests.

"I am calling on my people: don't fall for this trap. This is not an innocent environmental action," Erdogan said.

In late May and June last year, hundreds of thousands of Turks took to the streets denouncing Erdogan's increasingly autocratic leadership and demanding more democratic freedoms. The protests were sparked by opposition to government plans to uproot trees at Taksim Square's Gezi Park and build a shopping centre.

Fanned by outrage over the often brutal reaction by police, the demonstrations soon spread to other cities and developed into Turkey's biggest protests in decades. Thousands were wounded and at least 12 people have died in anti-government protests in the past year.

A group of architects, environmentalists and city planners who oppose Gezi Park's development said its members would march to Taksim despite the ban.

"If you go there, our security forces are under strict orders, they will do whatever is necessary from A to Z," Erdogan said in a speech in Istanbul. "You won't be able to go to Gezi like the last time. You have to obey the laws. If you don't, the state will do whatever is necessary."

Protests were also expected in Ankara, Izmir and other cities.

Ahead of the protests, CNN correspondent Ian Watson was detained briefly during a live a broadcast. He said that police had kneed him and that an officer later apologized.

A report this week by the Paris-based International Federation for Human Rights said that more than 5,600 demonstrators were being prosecuted for involvement in the protests while no one responsible for the violence against protesters had been sentenced.

The Turkish authorities "are actively engaging in a witch hunt against those who participated in the protests or spoke out," said the federation's president, Karim Lahidji.

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Suzan Fraser reported from Ankara, Turkey.

News from © The Associated Press, 2014