ANKARA/ISTANBUL - Turkey's deputy prime minister said on Monday the armed forces could be called up if needed to help quell popular protests that have swept Turkish cities in the last two weeks, the first time the possibility of a military role has been raised.Bulent Arinc made the remarks in Ankara, where 1,000 striking trade union workers faced off briefly against police backed by several water cannon, before police retreated and the crowd dispersed.In Istanbul, the cradle of protests that have presented Prime Minister Tayyip Erdogan with the greatest public challenge to his 10-year leadership, several hundred union members also marched in sympathy with the anti-government protests.Police prevented them entering Taksim Square, the focus of the unrest, which flared up again at the weekend with some of the fiercest clashes so far when police fired teargas and water cannon to clear thousands of people, some of them throwing stones, from the square."Our police, our security forces are doing their jobs. If it's not enough, then the gendarmes will do their jobs. If that's not enough ... we could even use elements of the Turkish Armed Forces," Arinc told Turkey's state-run TRT television.Any use of the army would be a dramatic step in Turkey, where Erdogan has pushed through democratic reforms including taming a military that toppled four governments in four decades.Monday's marches were peaceful but small compared with many of the recent protests, and, while it was unclear how many of the 850,000 or so public workers answered their unions' call to strike on Monday, there were no signs of major disruption.Police detained 441 people in connection with the clashes in Istanbul on Sunday and 56 in the capital Ankara. As violence across several cities entered its 18th day, at least four people have been killed and around 5,000 injured, according to the Turkish Medical Association.What began as a small demonstration by environmentalists upset at government plans to build on a public park adjoining Taksim has grown into a movement against Erdogan, who opponents say is overbearing and meddles too much in their personal lives.