Protesters gathered in a street in Tehran on Friday, 9 January | MAHSA / Middle East Images / AFP via Getty Images Iran has warned it will retaliate if attacked by the US, as protesters defied a deadly government crackdown on Saturday night. Videos verified by the BBC and eyewitness accounts appeared to show the government ramping up its response to the protests, which have spread to more than 100 cities and towns across every province in Iran. Medics at two hospitals have told the BBC that...