US President Barack Obama has ensured the world that “strong and smart” steps are being taken to defeat terrorism, in the wake of the deadly San Bernardino shootings.

Speaking in a prime time address from his Oval Office – only the third of his Presidency – Mr Obama said the San Bernardino attackers carried out a “new phase” of terrorism.

“This was an act of terrorism, designed to kill innocent people,” Mr Obama said.

“Let’s not forget that freedom is more powerful than fear.”

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Detailing ongoing anti-terrorism measures, Obama called on Americans not to give into that fear.

“The threat from terrorism is real but we will overcome it. We will destroy ISIL and any other organisations that tries to harm us,” he said, using an alternative name for the Islamic State terrorist group.

The alleged killers, an American Muslim, Syed Rizwan Farook, and his Pakistani-born wife, Tashfeen Malik, appeared to have been radicalised, but not to have belonged to an organised terrorist group, Obama said.

A couple embraces following the shooting that killed 14 people in San Bernardino. Photo: AAP

Obama said the Muslim couple “had gone down the dark path of radicalisation”, embracing a perverted interpretation of Islam that calls for war against America and the West.

“They had stockpiled assault weapons, ammunition and pipe bombs. So this was an act of terrorism,” he said.

He called for tougher gun controls, starting with a ban on gun purchases for anyone on a US government no-fly list.

“To begin with, congress should act to make sure no one on a no-fly list is able to buy a gun,” he said.

“What could possibly be the argument for allowing a terrorist suspect to buy a semiautomatic weapon? This is a matter of national security.”

Only days after the deadly attack, US Congress blocked a measure to subject those on the no-fly list to be barred from purchasing guns.

Some expected Mr Obama to announce an escalation in measures against Islamic State in Syria, however he assured those watching that current bombing attacks were doing a good job.

“We should not be drawn once more into a long and costly ground war in Iraq or Syria; that’s what groups like ISIL want,” he added.

“They know that if we occupy foreign lands they can maintain an insurgency for years, killing thousands of our troops and using our presence to draw new recruits.”

“We will prevail by being strong and smart.”