Warning of a new phase of terrorism, President Barack Obama vowed Sunday to pursue a muscular new approach to "destroy" the Islamic State and the spreading cancer of terror that has manifested in attacks in California and Tennessee.

In a forceful speech from the Oval Office, Obama called the Islamic State a group of “thugs and killers” and vowed several times to eradicate the group. He also urged Congress to authorize the expanded use of force against the terror group, which has a foothold across giant swaths of Iraq and Syria.

Obama’s address comes four days after a husband-and-wife team killed 14 people in San Bernardino, Calif. in what the FBI said could be an attack linked to the Islamic State. The president bluntly described the killings as an “act of terrorism designed to kill innocent people.”

"The terrorist threat has evolved into a new phase," Obama said, also citing the attacks that left five dead at two military facilities in Chattanooga, Tenn. "I know that after so much war, many Americans are asking whether we are confronted by a cancer that has no immediate cure."

He called for stronger screening of people in the U.S. without visas and encouraged lawmakers to pass legislation restricting people on “no-fly” lists from buying firearms.

Obama drew the line, though, at the call for a significant ramp-up in troops to assault the Islamic State from the ground, saying "we should not be drawn once more into a long and costly ground war in Iraq and Syria.”

And he expressed concern about rhetoric against Muslims, a group who he said are among America's staunchest allies.

"We cannot turn against one another by letting this fight be defined as a war between America and Islam. That, too, is what groups like ISIL want," he said, using an acronym for the Islamic State. "ISIL does not speak for Islam. They're thugs and killers. Part of a cult of death."