In an address to the nation in which he affirmed a belief that the United States would "destroy" ISIS and urged Americans not to give into fear, President Obama acknowledged a "new phase" of terrorist attacks including last week's shootings in San Bernardino.

"As we've become better at preventing complex multifaceted attacks like 9/11," Obama said, "terrorists turn to less complicated acts of violence like the mass shootings that are all too common in our society. It is this type of attack that we saw at Fort Hood in 2009, in Chattanooga earlier this year, and now in San Bernardino."

"This is a matter of national security."

"And as groups like ISIL [ISIS] grew stronger amidst the chaos of war in Iraq and then Syria, and as the internet erases the distance between countries, we see growing efforts by terrorists to poison the minds of people like the Boston Marathon bombers and the San Bernardino killers."

Obama said he will "urge high-tech and law enforcement leaders to make it harder for terrorists to use technology to escape from justice," without going into details, and order a review of the visa waiver program that allowed one of the San Bernardino terrorists into the US. Obama also called on Congress to ban people on no-fly lists from buying guns. "What could possibly be the argument for allowing a terrorist suspect to buy a semi-automatic weapon?" he asked. "This is a matter of national security."

More generally, Obama also called for greater restrictions on assault weapons. "We also need to make it harder for people to buy powerful assault weapons like the ones that were used in San Bernardino," he said. "I know there are some who reject any gun safety measures, but the fact is that our intelligence and law enforcement agencies, no matter how effective they are, cannot identify every would-be mass shooter, whether that individual was motivated by ISIL or some other hateful ideology. What we can do and must do is make it harder for them to kill."