Investigators believe the woman suspected in the killings of 14 people in San Bernardino, Calif., pledged her support to the Islamic State in Iraq and Syria (ISIS) during the attack, according to multiple reports.
Three officials told CNN that Tashfeen Malik, 27, made a Facebook post as the attack was happening pledging her allegiance to ISIS leader Abu Bakr al-Baghdadi.
The White House refused to confirm reports.
“There is information that has been disseminated, but I’m not going to be in a position to confirm it," White House press secretary Josh Earnest said. “The FBI is leading this investigation, as the president said yesterday, because of the possibility this was a terrorist attack.”
Malik and her husband, Syed Rizwan Farook, 28, are suspected of storming an office building on Wednesday, where 14 people were killed and 21 others were wounded. The couple was later killed in a shoot-out with police.
Authorities have been trying to determine the motive behind the attack, with questions raised about whether the shootings were an act of terroristm, workplace violence or some kind of combination.
The killings did not fit neatly into the patterns of Islamic terrorism; the target in this case was a small county government site in a relatively unfamiliar part of the country.
Malik's participation in the shootings was also unusual, as was the fact that the violence was carried out by a married couple, who had dropped off their six-month-old daughter with her grandparents.
The shootings may also inflame the congressional debate over visitors to the United States.
Law enforcement officials said Farook made two trips to Saudi Arabia, first in 2013 for the Muslim pilgrimage Hajj and then to marry Malik, whom he met online. Malik then came to the U.S. on a fiancé visa and later became a permanent resident.
Authorities said Farook may have been radicalized by his wife. He was reportedly briefly in contact via phone and social media with one person being investigated for possible international terrorist connections.
Farook worked as a restaurant inspector for San Bernardino County, and many of those killed or wounded by the couple at the Inland Regional Center were his colleagues.
The House has already approved legislation placing new restrictions on the resettlement of Syrian refugeess in the United States, and is expected to consider a measure tightening the rules for people travling to the country under the Visa Waiver Program.
A day after the shooting, President Obama said it remained unclear whether it was an act of terrorism. He also argued that ISIS did not represent an "existential threat" to the United States.
Colleagues of Farook told the Los Angeles Times that he was a devout Muslim, but rarely spoke of his faith in the workplace. Farook’s family said they had no idea he had become radicalized.
The couple allegedly used .223 rifles – illegal in California — to carry out the attack on the Inland Regional Center, which provides social services to people with developmental disabilities.
Police found thousands of rounds of ammunition and 12 pipe bombs at the couple’s home, as well as tools to make improvised explosive devices (IEDs).
This story was updated at 11:57 a.m.