ISTANBUL - An unknown assailant shot the deputy mayor of Istanbul's Sisli district in the head on Monday and he was in a critical condition, Turkish broadcaster NTV reported.It was not immediately clear whether the incident was linked to Friday's abortive military coup in which more than 200 people were killed. Turkey remains in a state of high tension, though the government says it has the situation fully under control.NTV reported that the assailant had entered the office of deputy mayor Cemil Candas and then gun shots were heard. Turkey's main opposition Republican People's Party (CHP) runs the prosperous Sisli district. Along with other opposition parties the CHP has condemned the attempted coup.Turkey purged its police on Monday after rounding up thousands of soldiers in the wake of a failed military coup, and said it could reconsider its friendship with the United States unless Washington hands over a cleric Ankara blames for the putsch.Turkish authorities moved swiftly to retaliate for Friday night's coup, in which more than 200 people were killed when a faction of the armed forces tried to seize power.But the swift justice, including calls to reinstate the death penalty for plotters, drew concern from Western allies who said Ankara must uphold the rule of law in the country, a NATO member that is Washington's most powerful Muslim ally.Thousands of members of the armed forces, from foot soldiers to commanders, were rounded up on Sunday, some shown in photographs stripped to their underpants and handcuffed on the floors of police buses and a sports hall. Several thousand prosecutors and judges have also been removed. A senior security official told Reuters that 8,000 police officers, including in the capital Ankara and the biggest city Istanbul, had also been removed from their posts on suspicion of links to Friday's coup bid.Thirty regional governors and more than 50 high-ranking civil servants have also been dismissed, CNN Turk said.Prime Minister Binali Yildirim said 7,543 people had so far been detained, including 6,038 soldiers. Work was under way to purge the civil service.Turkey blames the failed coup on Fethullah Gulen, a cleric based in the United States who has a wide following in Turkey and denies any involvement.Ankara has demanded Washington hand him over. Washington says it is prepared to extradite him but only if Turkey provides evidence linking him to crime. Yildirim rejected that demand."We would be disappointed if our (American) friends told us to present proof even though members of the assassin organization are trying to destroy an elected government under the directions of that person," Yildirim said."At this stage there could even be a questioning of our friendship," Yildirim added.Yildirim said 232 people were killed in Friday night's violence, 208 of them civilians, police and loyalist soldiers, and a further 24 coup plotters. Officials previously said the overall death toll was more than 290.