Kerry made the comments as he left al-Quds for Jordan and Saudi Arabia to discuss his effort to broker peace between Israelis and Palestinians, saying that he was confident the government of Iraqi PM Nouri Maliki could defeat the militants, BBC reported on Sunday.
"We will stand with the government of Iraq and with others who will push back against their efforts to destabilize," Kerry said.
"We are not contemplating putting boots on the ground. This is their fight."
Iraqi officials said they have lost control of Fallujah to the militant group, the Islamic State in Iraq and the Levant, known as ISIL.
The head of the police in Anbar province - Hadi Razeij - said on Saturday that his men had pulled back to the city walls and the people of Fallujah were "the prisoners of ISIL".
Fighting there erupted after troops broke up a protest camp by Sunni Arabs in the city of Ramadi on Monday.
In recent months, Sunni militants have stepped up attacks across Iraq, raising fears of a return to full-scale conflict in the war-stricken country.
On Wednesday, the United Nations said at least 7,818 civilians and 1,050 members of the security forces had been killed in 2013 and the annual death toll was the highest in years.
NTJ/HH