President Obama on Sunday night acknowledged that the U.S. is "at war with terrorism" following a series of deadly terror attacks on American soil and around the world, and sought to assure Americans that the growing global terror threat will be defeated.

Obama spoke four days after terrorists apparently associated with ISIS fatally shot 14 people and wounded 21 more in San Bernardino, Calif. Those attacks came 19 days after a series of shootings and suicide bombings in Paris killed 130.

"This was an act of terrorism designed to kill innocent people," Obama said of the San Bernardino shooting in his first Oval Office address since 2010. "I am confident we will succeed in this mission because we are on the right side of history."

The president said the San Bernardino attack was inspired by ISIS, but added that it does not appear connected to a larger terror network.

Authorities say a Muslim husband-wife team carried out the attack and that the wife pledged allegiance to ISIS and its leader in a Facebook post.

Though Obama said there was no evidence that the shooters were directed by a terror network overseas or that the attack was part of a broader plot, he noted the couple "had gone down the dark path of radicalization."

He also acknowledged in his 13-minute address that the global terror threat has entered a "new phase."

The president offered no new or specific changes to the military campaign in Iraq and Syria to defeat ISIS, which has claimed responsibility for the Paris attacks and several other smaller-scale attacks in recent weeks.

However, Obama called on Congress to tighten America's visa waiver program and to pass a new authorization for military actions already underway against ISIS in Iraq and Syria.

The effort so far has been a U.S.-led bombing campaign, non-combat U.S. support troops in Iraq and roughly 50 Special Forces members in Syria.

Obama also reiterated his call for tightening U.S. gun laws, saying no matter how effective law enforcement and intelligence are, they can't identify every would-be shooter. He said such a move is a matter of national security to prevent potential killers from getting guns.

"People are really scared," Republican presidential candidate and Florida Sen. Marco Rubio said afterward. "Nothing in this speech tonight is going to assuage people's fears."

He also said Obama offered "nothing new" and that tighter gun control would not have prevented the San Bernardino attack.

Obama has been criticized for years for what critics say is his failure to recognize the growing threat of ISIS, calling the group a "JV team" and saying the Paris attacks were just a "setback" in the fight against extremism.

"I know that after so much war, many Americans are asking whether we are confronted by a cancer that has no immediate cure," he said, speaking from a lectern in his West Wing office.

While Obama has spoken frequently about ISIS in recent news conferences and at other events, the decision to speak in prime-time reflected concern among his advisers that his message isn't breaking through.

The White House has been particularly concerned about the heated rhetoric from Republican presidential candidates about Muslims.

Obama implored Americans to not turn against Muslims at home, saying ISIS was driven by a desire to spark a war between the West and Islam. However, he also called on Muslims in the U.S. and around the world to take up the cause of fighting extremism.

The spread of radical Islam, Obama said, is "a real problem that Muslims most confront without excuse." And he said that Muslims in America must not be treated differently.

"If we do that we lose," Obama said.

The Associated Press contributed to this report.