Two of Turkey\'s main trade unions began a nationwide strike Monday to protest at police violence against anti-government demonstrators, a day after Prime Minister Recep Tayyip Erdogan defended his crackdown on an Istanbul protest park. Turkish Interior Minister Muammer Guler condemned the stoppage as \"illegal\" and warned strikers not to take to the streets, as the Islamic-rooted government battled to clamp down on nearly three weeks of nationwide civil unrest. Riot police were still firing volleys of tear gas and water at pockets of demonstrators in Istanbul and the capital Ankara early on Monday, after a weekend of clashes sparked by the eviction of protesters occupying Gezi Park, the epicentre of the protest movement. Nearly 600 people were arrested in the scuffles on Sunday alone, according to the Ankara and Istanbul bar associations. The KESK and DISK trade unions, who together represent hundreds of thousands of workers, called a one-day stoppage to object to the police response to the trouble and said they planned to hold demos in the late afternoon. \"Our demand is for police violence to end immediately,\" KESK spokesman Baki Cinar told AFP, adding that the unions would be joined by striking engineers, dentists and doctors. The weekend violence has intensified a crisis that poses the biggest challenge yet to Erdogan\'s decade-long rule. At a rally of more than 100,000 supporters of his ruling Justice and Development Party (AKP) on Sunday, the premier insisted it was his \"duty\" to order police to storm Gezi Park after protesters defied his warnings to clear out. \"I said we were at an end. That it was unbearable. Yesterday the operation was carried out and it was cleaned up,\" a combative Erdogan told a sea of flag-waving loyalists. \"It was my duty as prime minister.\" Erdogan\'s words were met with roaring approval from the audience, the largest crowd to assemble since the crisis began. Many chanted: \"The people are here, where are the looters?\", using Erdogan\'s description of the demonstrators. At the same time, riot police were fighting running battles with thousands of protesters determined to regroup after being ousted from Gezi Park and the adjoining Taksim Square, a mere 10 kilometres (six miles) away from the AKP rally. Turkey\'s political turmoil first began when a peaceful sit-in to save Gezi Park\'s 600 trees from being razed prompted a brutal police response on May 31, spiralling into countrywide demonstrations against Erdogan. The crisis has claimed four lives and injured nearly 7,500 people so far, according to the Turkish Medical Association. The KESK and DISK union federations already held a two-day strike in support of the demonstrators two weeks ago, when thousands of workers poured into the streets. Opponents accuse Erdogan of authoritarian tendencies and of forcing Islamic conservative reforms on the mainly Muslim but staunchly secular nation of 76 million. But the 59-year-old, who has been in power since 2002, remains hugely popular. His AKP has won three elections in a row and took nearly half the vote in 2011, having presided over strong economic growth. Saturday evening\'s intervention in Gezi Park, where a festive tent city of protesters had sprung up, saw officers with gas masks and riot shields storm the patch of green, sending thousands of campers scrambling to escape clouds of acrid tear gas. Many sought refuge in the luxury hotels surrounding the park, whose lobbies did not escape bursts of pressurised water as guests choked on tear gas fumes. Thousands held demos in other cities in support of the Gezi Park campers. The Taksim Solidarity group, seen as most representative of the protesters, said \"hundreds\" had been injured in the Gezi Park unrest, while Istanbul governor Huseyin Avni Mutlu put the number at 44. \"Gezi Park and Taksim Square have been evacuated and returned to the people,\" Erdogan told the party faithful on Sunday. By Monday morning, police were still guarding the park and nearby Taksim Square, but with a much smaller presence than at the weekend. They reopened the newly spruced-up square, allowing morning commuters to cross the space as traffic flowed freely, though the park remained sealed off. Erdogan has taken a tough line on the protesters throughout, but in a bid to end the unrest he made an unexpectedly conciliatory gesture on Friday, when he offered to suspend the Gezi project pending a court ruling on its legality. But the Taksim Solidarity group rejected the olive branch, saying the government had failed to address all their demands, which include a call for arrested demonstrators to be released and for police chiefs in cities that saw clashes to be sacked. The United States and other Western allies, along with human rights groups, have widely criticised Erdogan\'s handling of the crisis.