By Jeff Mason WASHINGTON, May 25 (Reuters) - Vice President Joe Biden reassured Iraqi Prime Minister Haidar al-Abadi of the U.S. commitment to help fight Islamic State militants in an effort at damage control on Monday after Defense Secretary Ash Carter questioned Iraqi troops' desire to fight. Carter told CNN on Sunday that Iraqi forces showed no will to battle against Islamic State militants during the fall of Ramadi a week ago, and U.S.