WRAPUP 4-Russian mercenaries return to base after deal ends mutiny
* Adds Putin in paragraphs 4-6, Chinese support * Kremlin says mercenary leader will move to Belarus * Wagner fighters leave Rostov, regional governor says * Belarus says brokered deal in return for rebels' safety ROSTOV-ON-DON/VORONEZH, Russia, June 25 (Reuters) - H eavily armed Russian mercenaries withdrew from the southern Russian city of Rostov overnight under a deal that defused an unprecedented challenge to the authority of President Vladimir Putin and halted their rapid advance on Moscow.