Turkish police detain up to 100 protesters in support of Istanbul mayor -- media outlet / Turkish police arrest Istanbul's mayor, a key Erdogan rival / Turkey police arrest Istanbul mayor, key rival to President Erdogan / Key Erdogan rival arrested by Turkish police as government crackdown escalates / Police arrest Istanbul mayor, a key Erdogan rival, over alleged corruption and terror links / Turkish police arrest Istanbul mayor, a key Erdogan rival, as government crackdown escalates / Police arrest Istanbul mayor and key Erdogan rival amid crackdown / Turkish police detain Erdogan's main political rival / DEVELOPING -- Turkish police reportedly detain Istanbul Mayor Ekrem Imamoglu, one of President Recep Tayyip Erdogan's main rivals