By Humeyra Pamuk ANKARA (Reuters) - Turkey has extended a purge of official bodies to the banking and telecoms regulators and state TV, firing dozens of executives in moves that appear to broaden Prime Minister Tayyip Erdogan's backlash against a corruption investigation. The authorities have already sacked thousands of police officers, dozens of prosecutors and some state television officials in response to the corruption investigation, which has become the biggest challenge to Erdogan's 11-year rule.