WASHINGTON (Reuters) - Vice President Joe Biden reassured Iraqi Prime Minister Haidar al-Abadi of the United States' commitment to Iraq's fight against Islamic State militants on Monday after the US defense chief questioned Iraqi troops'will to fight.

Mr Biden used the call to "reaffirm U.S. support for the Iraqi government's fight against ISIL," the White House said in a statement, referring to the group by an acronym.

"The vice president recognized the enormous sacrifice and bravery of Iraqi forces over the past eighteen months in Ramadi and elsewhere," it said.

US Defense Secretary Ash Carter told CNN on Sunday that Iraqi forces showed no will to fight against Islamic State militants during the fall of Ramadi a week ago, and US forces were trying to encourage them to engage more directly.