FBI Director James Comey Jr. has warned that there are more terrorist organisations planning to attack the homeland at this time than there were before the Sept. 11, 2001 al-Qaeda launched terrorist attacks in three U.S. cities that killed nearly 3,000 people.

During a Senate FBI oversight hearing on Wednesday, Comey told Sen. Lindsey Graham that the terror groups' ability to have a safe haven increases their ability to launch sophisticated attacks against the United States, according to CNN.

Comey made the remarks after the South Carolina Republican asked him of his assessment of the terrorist organisations and the possibility of them carrying out another deadly attack on American soil similar to 9/11.

The discussion was a result of the recent attack in San Bernardino Inland Regional Center by a terrorist couple who killed 14 people, and other terrorist attacks outside the country, including that in Paris that left 130 dead.

The FBI director blamed budget cuts imposed by Congress as having affected the agency's resources and ability to protect America from terrorists.

He said the likelihood of another 9/11 attack against the homeland is not too remote unless the caliphate in Syria and Iraq is destroyed.

According to Comey, the attack in San Bernardino was "an act of terrorism committed by people radicalised by organisations at least inspired by the Islamic State."

He also made a swipe at the recent statements made by Republican presidential front-runner Donald Trump against banning Muslims from travelling to the U.S., saying "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.''

Earlier, following the shooting in San Bernardino, California, President Obama acknowledged that terror threat in the U.S. has "entered a new phase,'' claiming that this time, it seeks to "poison the minds of people here and around the world.''

"I know that after so much war, many Americans are asking whether we are confronted by a cancer that has no immediate cure," he said, AP reported. "The threat from terrorism is real, but we will overcome it.''

Obama said that while there was no evidence the shooters were directed by a terror network overseas or part of a broader plot, "the two of them had gone down the dark path of radicalisation."