President Barack Obama has delivered a rare Oval Office address after the last week’s San Bernardino attack that left 14 dead.

Barack Obama said the killings were “an act of terrorism designed to kill innocent people”.

“Freedom is more powerful than fear,” the president said, warning that falling prey to divisiveness in American society would play into the hands of extremists.

Barack Obama also said the US must make it harder for potential attackers to obtain guns.

The president vowed that the US would overcome the evolving threat of terrorism, but warned that Americans “cannot turn against one another by letting this fight be defined as a war between America and Islam”.

“If we’re to succeed in defeating terrorism, we must enlist Muslim communities as some of our strongest allies, rather than push them away through suspicion and hate,” Barack Obama said.

He reminded his audience that Muslim-Americans were part of US society.

“And, yes, they are our men and women in uniform who are willing to die in defense of our country. We have to remember that,” he said.

Barack Obama warned that turning against America’s Muslim communities would be exactly what Islamist extremists in the so-called Islamic State group want.

The president told Americans that terrorism had entered a new phase, from large scale attacks by al-Qaeda to less complicated attacks by radicalized individuals.

He said the US would draw upon “every aspect of American power” to combat ISIS.

Barack Obama underscored that the US and its allies have increased their bombing of Islamic State oil infrastructure and would continue to train and equip moderate rebels in Iraq and Syria.

“Our military will continue to hunt down terrorist plotters in any country where it is necessary,” he said.

Barack Obama added that there are a number of things that can be done on home soil to combat terrorism.

He called for stricter gun control and said he had ordered the Departments of State and Homeland Security to review the K-1 fiancé visa program under which the female attacker in San Bernardino originally entered the US.

This was only the third Oval Office address of Barack Obama’s presidency – they are reserved for events of national importance.

Barack Obama’s speech was in response to a mass shooting by a married couple that left 14 dead.

Syed Rizwan Farook, 28, and his wife Tashfeen Malik, 29, opened fire on an office Christmas party and were later killed in a shootout with police.

In his speech, the president characterized ISIS as “thugs and killers”, adding: “The threat from terrorism is real, but we will overcome it.”

The group said in a radio broadcast that the couple that Syed Rizwan Farook and Tashfeen Malik were ISIS supporters, but gave no indication that ISIS was involved in the attack’s planning.

The FBI is also looking into reports Tashfeen Malik posted a message on Facebook pledging allegiance to ISIS around the time of the attacks.

Syed Rizwan Farook and Tashfeen Malik used handguns and semi-automatic weapons that had been legally purchased in the US, police say.

Bomb equipment, weapons and thousands of rounds of ammunition were later found in their home.

The San Bernardino attack is the deadliest mass shooting in the US since 26 people were killed at a school in Connecticut in 2012.

The authorities said there was no indication so far the killers were part of an “organized group or formed part of a broader terrorist cell”.