President Barack Obama speaks about counter-terrorism and the United States' fight against the Islamic State group during an address to the nation from the Oval Office of the White House in Washington, Dec. 6, 2015.
President Barack Obama speaks about counter-terrorism and the United States' fight against the Islamic State group during an address to the nation from the Oval Office of the White House in Washington, Dec. 6, 2015.

Following the recent attack in California, President Barack Obama has called on Americans not to give in to fear, while trying to assure the public that he and his administration take the threat of terrorism seriously.

In a rare speech from the Oval Office in the White House, Obama Sunday night said the FBI is still gathering facts about what happened last week in San Bernardino, California. He added there is no evidence yet that the two shooters involved were part of a broader terror network overseas.

He said the U.S. has hardened its defenses against terrorist threats and stressed the U.S. military has relentlessly pursued terrorist networks overseas.

But he noted that terrorists are now turning to what he called "less complicated" attacks like what happened in California.

Transcript of the President's Speech
Obama said he understands that Americans are asking if "we are confronted by a cancer that has no immediate cure." He vowed "we will destroy ISIL," using an acronym for the Islamic State terror group.

He promised the U.S. military will hunt down terrorist leaders in any country where they hide. He also said the U.S. will continue to provide training and equipment to Syrian and Iraqi forces fighting IS on the ground. And he said the U.S. is working with friends and allies, and that the international community has begun to pursue a timeline to bring and end to the Syrian war.

'Freedom is more powerful than fear'

Obama said he has ordered the Department of State and Homeland Security to review the visa waiver program under which the female shooter in California got into the United States.

He called on Congress to make sure no one on a no-fly list can buy a gun. And he said again that we must make it harder for people to buy assault weapons.

Yanira Perez (2-R) wipes her eyes as she and her m
Yanira Perez (2-R) wipes her eyes as she and her mother, Marcela, pay respects at a makeshift memorial to honor the victims of Wednesday's shooting rampage, Dec. 5, 2015, in San Bernardino, California.

The president said these are the steps we can take together to defeat the terrorist threat.

He added we should not be drawn once again into a long and drawn-out war on the ground in Iraq or Syria. He said that's what IS wants us to do.

Oval Office Addresses
He stressed that we cannot let this war be defined as a struggle between America and Islam. He said that, too, is what IS wants.

Watch Obama's comments on the US response to the terror threat:

Obama Discusses the US Response to Terrorism video player.

?The president said Muslim leaders must work with us to reject hateful ideology that al-Qaida and IS promote. He also said it is the responsibility of all Americans of every faith to reject the notion that Muslim Americans must be treated differently. He said that plays into the hands of IS.

He insisted "we are on the right side of history." And he said he is confident that we will win this fight against terrorism.

"Let's not forget that freedom is more powerful than fear," Obama added.

California rampage

U.S.-born Syed Rizwan Farook and his Pakistani wife Tashfeen Malik killed 14 people and wounded 21 at a gathering of local government workers last Wednesday in San Bernardino, about an hour's drive east of Los Angeles.

An undated combination of California Department of
An undated combination of California Department of Motor Vehicles photos shows Tashfeen Malik, left, and Syed Farook, the husband and wife who died in a gunbattle with authorities after a mass shooting in San Bernardino, Calif., Dec. 2, 2015.

 They also planted a pipe bomb that failed to go off before fleeing in a black sport utility vehicle. Their car was later spotted and they were killed as they exchanged gunfire with police.  Authorities found 12 pipe bombs, bomb making materials and thousands of rounds of ammunition in their home.

The Federal Bureau of Investigation is continuing to investigate what led Farook and Malik to carry out the California attack.

Lynch said investigators are "trying to learn everything" about the couple, "what led these two people to become murderers." She said authorities are tracking Malik's Pakistani background, her relationship with Farook and how they came to attack the site they did, a government center that offered services for developmentally disabled people.

But she said at this point, investigators do not believe the couple was part of a larger terrorist network.

WATCH: Related video on search of couple's apartment

Reporters Allowed in Home of Shooting Suspects video player.

The Islamic State group claimed on its English-language radio broadcast Saturday the two were its "soldiers," and in an Arabic broadcast called them "supporters."  The militant group did not explicitly claim responsibility for the attack.

Malik posted a message on Facebook around the time of the attack pledging allegiance to Islamic State.

Pledges of loyalty to IS leader Abu Bakr al-Baghdadi have been reportedly found in social media posts by others who carried out mass killings.  Some Islamic State supporters posted messages on Arabic social media hailing Wednesday's shootings and congratulating the killers.  Some promised more attacks in the United States.

The FBI said a number of pieces of evidence had turned up indicating that this was a terrorist act, including signs the massacre was extensively planned.  Investigators are also looking at two crushed cell phones the couple apparently threw away near the site of the killings.

Two attorneys representing the Farook family criticized the media for what they say is a rush to judgment that this was a terrorist attack simply because the suspects were Muslim.

A law enforcement officer looks over the evidence
A law enforcement officer looks over the evidence near the remains of a SUV involved in the Wednesday's attack is shown in San Bernardino, California, Dec. 3, 2015.