Iran's winning goal came through Morocco substitute Aziz Bouhaddouz, who put the ball into his own net with a 95th-minute diving header at the near post for a heartbreaking defeat for the North Africans.
"I'm feeling disappointed and if we had come out with a draw I would've also been disappointed considering the way the game played out," Renard told BBC Sport. "A defeat, when you had quite a few opportunities, it is the worst thing that could have happened in injury time.
"In a competition you have three matches to play and we still have two matches left. Whoever our opponents are, there is still hope.
"Of course the players are feeling down and we can only blame ourselves. It's our fault and it's my responsibility - we will have to prepare for the next two games really well.
"During the first 20 minutes we should have scored and these defeats, when they come in added time, are cruel."
Morocco, who sit bottom of Group B after the first round of games, return to action on June 20 when they take on Portugal.