Comey shared the information at a Senate FBI oversight hearing after Sen. Lindsey Graham questioned him on his agency's knowledge of terrorism.
"Do you agree with the following statement: There are more terrorist organizations with men, equipment and safe havens, along with desire to attack the American homeland, anytime since 9/11
?" the South Carolina Republican asked.
"I agree," Comey said.
Comey said budget cuts imposed by Congress in recent years have reduced the FBI's ability to protect America from terrorism.
"What do you think the likelihood of another 9/11 against the homeland will be if we don't destroy the caliphate in Syria and in Iraq in the next year?" Graham asked.
"That's certainly a hard question for me to answer," Comey said. But, he added, "Their ability to have a safe haven from which to gather resources, people, plan and plot increases the risk of their ability to mount a sophisticated attack against the homeland."
Comey's comments were made following several global terrorist attacks over the last month in France
, as well as the attack in San Bernardino, California
, last week which claimed the lives of 14 people.
Comey said the attack in San Bernardino
was an act of terrorism committed by people radicalized by organizations at least inspired by ISIS.
Comey added that "people who know better than I" agree that "fiery rhetoric" about Muslims puts the lives of American soldiers, diplomats and FBI agents in the Middle East in jeopardy, a reference that comes in the wake of controversial statements made by GOP presidential front-runner Donald Trump.