WASHINGTON (AFP) - US President Barack Obama will make an address to the nation on Sunday on counterterrorism efforts, the White House said, days after 14 people were shot dead in California.

The speech from the Oval Office will include "the steps our government is taking to fulfill his highest priority: keeping the American people safe," the White House said in a statement Saturday.

Obama vowed earlier Saturday that America "will not be terrorised," as the Islamic State group praised the couple behind Wednesday's mass shooting as "soldiers" of its self-proclaimed caliphate.

The FBI are investigating the attack in San Bernardino as a possible act of terrorism.

"The president will provide an update on the ongoing investigation into the tragic attack in San Bernardino," the White House statement said.

"The president will also discuss the broader threat of terrorism, including the nature of the threat, how it has evolved, and how we will defeat it.

"He will reiterate his firm conviction that ISIL (IS) will be destroyed and that the United States must draw upon our values - our unwavering commitment to justice, equality and freedom - to prevail over terrorist groups that use violence to advance a destructive ideology."