it happened to me too when i was in freezing weather. somehow the frozen water expanded something (hinge, plastic side molding on door). my dad kept pulling and pulling the door open, not knowing it pushed the fender in. i used a small crowbar with a piece of wood underneath for leverage. and gently pushed.
1999 Cherokee Sport 4x4, RE 3.5" SF, SYE, DS, and Monotubes, Pro Comp adj track bar. Soft 8s wrapped in 31x10.5x15 Dik Cepek Mud Countrys, Silverstars w/ HD harness, Class III rear hitch, Yakima snowboard racks, cool sunroof. NP231, C8.25, and D30.