WASHINGTON — President Obama sought on Sunday to calm a jittery American public after the terrorist attack last week in California, delivering a prime-time address designed to highlight the government’s campaign against an evolving threat.

Speaking from behind a lectern in the Oval Office, Mr. Obama bluntly acknowledged the heightened fears that followed attacks in Paris and in San Bernardino, Calif., and called the California assault an “act of terrorism” that appeared to have been inspired, but not directed, by members of the Islamic State in Iraq and Syria.

“The terrorist threat has evolved into a new phase,” Mr. Obama said. “I know that after so much war, many Americans are asking whether we are confronted by a cancer that has no immediate cure.”

He added, “The threat from terrorism is real, but we will overcome it.”
The president’s speech was not intended to announce a shift in strategy, or new policies to combat the terrorist threat at home and overseas. Rather, it was designed to inform Americans of the administration’s continuing efforts, and to urge Americans not to give in to fear.
In the prime-time speech, only his third from the Oval Office, Mr. Obama sought to reassure Americans by ramping up his public response to the massacre by a married couple in San Bernardino. He said officials would examine a visa program that let the wife into the United States, but he offered few significant changes to the nation’s homeland security.

“It is clear that the two of them had gone down the dark path of radicalization,” Mr. Obama said, noting that officials had little evidence of a plot directed by the Islamic State. “This was an act of terrorism designed to kill innocent people.”

But he also urged Americans not to give in to fear or resort to discrimination against Muslims or others in an effort to feel more secure. He called the Islamic State terrorists “thugs and killers, part of a cult of death,” but he said they did not speak for most Muslims.
Interactive Feature | How ISIS Expanded Its Threat The Islamic State emerged from a group of militants in Iraq to take over large portions of Iraq and Syria, and now threatens other countries in Europe and elsewhere.
“Muslim Americans are our friends and our neighbors, our co-workers, our sports heroes,” he said. “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.”

The rampage last week, which killed 14 people, was the first time that terrorists inspired by the Islamic State, also known as ISIS or ISIL, had successfully struck in the United States. It came shortly after theParis attacksassaults in Beirut, Lebanon; and the takedown of a Russian airliner over Egypt, all attributed to elements of the Islamic State.

For Mr. Obama, the arrival in the United States of successful attacks inspired by the Islamic State underscores urgent questions about the military and diplomatic effort initiated by his administration more than a year ago, when the group surged into Iraq, seizing territory there and in neighboring Syria.

The decision to address the American people from the Oval Office, a venue he has largely shunned during his presidency, reflected the gravity of a subject that has come to define Mr. Obama’s presidency, especially in his second term. And it suggested the importance that the president and his advisers have placed on responding to mounting criticism of his strategy to defeat the group.