President Obama on Sunday called the San Bernardino massacre "an act of terrorism designed to kill innocent people."
He said the married couple who committed the violence "had gone down the dark path of radicalization" but that there was no evidence yet that they were part of a larger terrorist organization.
The president also blasted the Islamic State "thugs and killers, part of a cult of death.... they account for a tiny fraction of...Muslims."
"ISIL does not speak for Islam," he added, urging Americans to unite and avoid discrimination.
His statements came as the investigation into the shooting rampage continued. The FBI on Saturday raided the home of one of shooter Syed Rizwan Farook's friends as agents searched for the source of the guns used in the attack. And in Pakistan on Sunday, the interior minister said the country has launched its own investigation and offered assistance to U.S. authorities.
In San Bernardino, residents tried to get back to their routines after what may be the deadliest act of terrorism on U.S. soil since 9/11. On Saturday, many residents resolved to get on with life but said they were still anxious.
"I'm nervous," said Fernandino Rodriguez, 39. "You hear ambulance and a firetruck sirens and you wonder: 'What happened now?' You're constantly in fear."
"I'm listening and watching for signs of trouble — sirens, even helicopters," added Dyesha McCrumb. "That's because I believe police still have not gotten to the bottom of this terrorist attack."
The FBI is investigating the shooting as an act of terrorism apparently inspired by the extremist group Islamic State.
U.S. Atty. Gen. Loretta Lynch urged the public Sunday not to jump to conclusions about the motive for the attack or the couple's ties to ISIS. She said Farook had made contact with some people the FBI was monitoring but again stressed the investigation is ongoing.
"I would caution people not to try and define either of these two individuals right now," she said on NBC's "Meet the Press."
Obama's address comes amid growing criticism from Republicans and even some Democrats about his policies for combating terrorism and dealing with Syria's civil war, especially after last month's coordinated Islamic State attacks in Paris that killed 130 people.
San Bernardino is one of several attacks in recent years, including the 2013 Boston Marathon bombings, that appear to involve "lone wolf" assailants in the United States who are inspired by terrorist groups but act independently. Experts say such cases pose a particular problem for authorities because the attackers are already in this country and are more difficult to detect than terrorists coming here from abroad.
Since taking office in 2009, Obama has only addressed the nation twice from the Oval Office, the symbol of White House power. The most recent was Aug. 31, 2010, when he announced the withdrawal of all U.S. troops from Iraq in keeping with his campaign promise to end the war there.
Five years later, that speech appears a bittersweet moment in history.
Over the last year and a half, Obama has sent about 3,500 troops back to Iraq to train and advise local security forces in the fight against Islamic State.
He is under intense pressure to further escalate the effort to break a yearlong military stalemate with the group, which continues to control vast amounts of territory, including key cities in Iraq and Syria.
Secretary of Defense Ashton Carter has announced that about 200 more special operations troops would be sent to Iraq to conduct raids and help step up airstrikes.
Although the militants have lost ground in recent months due to counterattacks and intense bombing, they have expanded their global reach by conducting a deadly attack in Paris, downing a Russian passenger jet over Egypt and building up a new stronghold in Libya.
In the fiercely contested 2016 presidential race, Republican candidates have excoriated Obama's counter-terrorism efforts as weak and ineffective, and called for stopping or restricting immigration into the U.S. of Syrian refugees and others.
In a statement announcing the speech, set for 8 p.m. EST, the White House said Obama will seek to reassure the public that the government is taking effective steps to ensure the nation's safety.
Obama "will reiterate his firm conviction that [Islamic State] will be destroyed," a White House spokesman said.
Authorities now believe Farook and his wife, Tashfeen Malik, were inspired by militant appeals on the Internet.
Earlier Saturday, after Obama had been briefed by Lynch, FBI Director James B. Comey and other senior law enforcement and intelligence officials, the White House said authorities still had not turned up any evidence indicating the couple were part of a terrorist network.
FBI technicians are trying to reconstruct their digital footprints from partially destroyed computer hard drives, cellphones and their online accounts.
They also are searching for signs the couple may have communicated using encryption to hide their messages.
The couple had not drawn the attention of the FBI or other federal authorities that seek to identify and track potential terrorists, even though Farook had used the Internet to make contact with people from the Shabab, an Islamist militant group based in Somalia, and Al Nusra Front, an Al Qaeda-linked group in Syria, a federal law enforcement official said.
Malik was a onetime "modern girl" who became deeply religious during college and began posting extremist messages on Facebook after arriving in the U.S., a family member in Pakistan said in an interview with The Times. The relative in Malik's hometown of Karor Lal Esan, who asked to not be identified, said Malik's postings on Facebook were a source of concern for her family.
"She started taking part in religious activities and also started asking women in the family and the locality to become good Muslims," the family member said.
Two students who attended university with Malik confirmed that during her time at Bahauddin Zakariya University in Multan, Pakistan, she began attending Al Huda, a chain of modern institutes of Islamic education which mainly focuses on women with the stated objective of "bringing them back to their religious roots."
"She used to go to attend sessions in Al Huda almost every day," said a fellow student, who did not want to be identified. "She was not too close to any class fellow. She never shared her thoughts on religious issues with her fellow classmates in the department of pharmacology, where Malik studied. "We all are in a state of shock."
Experts said that the majority of women who attend Al Huda institutes, located in large cities, wear the hijab, a scarf covering worn by some Muslim women to cover the hair on the top of their head. They are usually well-heeled. These institutes use the group-isolating Islamic preaching session (called 'dars') activity to reinvent personal identity through 'discovery' of Islam.
Dr Ayesha Siddiqa, a Pakistani security analyst, said Al Huda institutes teach women "fundamentalist" ideas, though it is not necessarily a jihadist curriculum. "I call Al Huda the fourth generation of religious seminaries. It does not promote use of violence but takes you closer to the red line. Now, it is a personal decision to cross the red line and take or give one's life."
She said that the impact of such institutes is widespread, because a family that has a child going to a seminary has an impact on the thinking of other members of the family. "People would be familiar with, for instance, a daughter going to an Al Huda changing the mother and eventually the entire household. This dynamic is mirrored in more traditional seminaries as well."
For the last several days, supporters of Islamic State have used Twitter to praise the lethal attack in San Bernardino, but no official statement from the group appeared until Saturday.
U.S. intelligence analysts have no reason to doubt the authenticity of an Islamic State online broadcast Saturday that claimed last week's rampage was carried out by supporters, an American official said.
The broadcast on the group's official radio station said of the couple, "We pray to God to accept them as martyrs," but did not claim Islamic State had played a role in planning the attack.
Farook's father told the Italian newspaper La Stampa on Sunday that his son agreed with the ideology of ISIS leaders and was "obsessed" with Israel.
But a family representatives said Sunday afternoon that the shooter's father did not recall the comments he made the the publication.
Hussam Ayloush, executive director of CAIR in the greater Los Angeles area, said the father, like the rest of the family, is "dealing with a lot of stress."
"He's on medication," he said. "He doesn't recall saying that."
Neither Ayloush nor family attorney Mohammad Abuershaid would specify what the medication was or what condition it was used to treat.
The attorney said the family wants to "cooperate as much as they can" with the federal investigation.
Ayloush said that when he asked the father about the interview this morning, he said, "Which interview? ... I didn't speak to any media ... I didn't say any of that."
Meanwhile, the investigation into the San Bernardino attack continued. On Saturday, FBI agents raided the home of a friend of Farook's as the agency tried to determine whether the man had purchased two of the semiautomatic rifles used in the massacre, according to a law enforcement source.
The source, who asked to remain anonymous because the case is ongoing, said the FBI was seeking to interview Enrique Marquez Jr., who lived at the home, though it was not clear he had anything to do with the violence or knew what Farook did with the guns.
Neighbors said Marquez and Farook appeared to be good friends. Farook, his mother and siblings lived next door for several years before moving out a few months ago.
Family members and friends said they were stunned by the rampage, saying the couple showed no outward signs of radicalism.
They met on a dating website. The couple were married in Islam's holy city of Mecca in Saudi Arabia last year. The Saudi Embassy in Washington confirmed that Farook spent nine days in the kingdom in the summer of 2014. The couple's daughter was born in May, according to records.
Farook and Malik had amassed an arsenal of 2,000 9-millimeter rounds, 2,500 .223-caliber rifle rounds and "hundreds of tools" that could have been used to make explosive devices, authorities said.
The couple fired at least 65 shots when they stormed a party at the Inland Regional Center, where about 80 of Malik's co-workers at the San Bernardino Department of Public Health had gathered. Twelve of the 14 dead and 18 of the 21 injured were county employees, police said.
Hours later, the couple exchanged gunfire with police on San Bernardino streets, in a battle that launched bullets into homes and terrified residents.
Tanfani reported from Washington, Esquivel from Riverside and Sahagun and Parvini from Los Angeles. Times staff writers Richard Winton, Tony Barboza, Marisa Gerber, Rong-Gong Lin II, Cindy Carcamo and Dexter Thomas in Los Angeles; and Brian Bennett, Richard A. Serrano and David S. Cloud in Washington; and Aoun Sahi in Islamabad, Pakistan, contributed to this report.
MORE ON SAN BERNARDINO SHOOTING