May 31 (Bloomberg) -- Turkish authorities shut down transportation and thousands of police descended on Istanbul’s central square in a show of force by Prime Minister Recep Tayyip Erdogan on the anniversary of the Gezi Park protests.

Erdogan, 60, is seeking to prevent a repeat of last year’s events, which spiraled from an environmental sit-in into more than two weeks of nationwide anti-government demonstrations that sent millions into the streets and markets tumbling. Erdogan says those protesting against him in his 12th year in office aren’t sincere and won’t be allowed to gather in public spaces.

“Security forces have received an order,” Erdogan said today in a speech in the neighborhood of Sultangazi, referring to calls for demonstrations today. “They’ll do what’s necessary from A to Z.”

Ivan Watson, a reporter for CNN, was detained during a live broadcast as he reported from Taksim Square, where riot police were joined by hundreds of plainclothes officers brandishing truncheons and carrying black backpacks. Some 25,000 police were appointed for the day, according to Hurriyet newspaper. Istanbul’s metro was closed and police vehicles blocked off roads to Taksim.

Erdogan, who has weathered social tensions over his rule amid allegations of corruption and increasing authoritarianism, is preparing his party for the nation’s first-ever direct presidential elections on August 10. While Erdogan is widely expected to run for the position, no politician from either his ruling Justice and Development Party or the main opposition parties has yet announced a candidate.

To contact the reporter on this story: Benjamin Harvey in Istanbul at [email protected] To contact the editors responsible for this story: Benjamin Harvey at [email protected] Kevin Costelloe, Peter Chapman