US officials have said that the female shooter responsible for the mass shooting in San Bernardino, California, with her husband was a member of ISIS.
If the ISIS link is proven to be true, this will represent the first ISIS attack on American soil.
Tashfeen Malik, who burst into a staff Christmas party with Syed Rizwan Farook, wielding assault rifles, pledged allegiance to ISIS leader Abu Bakr al-Baghdadi on Facebook, according to officials investigating the attack in San Bernardino, California.
The motive behind their deadly killing spree has still not been confirmed while investigators work to determining whether the couple’s act was terrorism-related.
The post on social media by Malik on Wednesday was done on an account with a different name, according to one US official – but investigators did not explain how they knew she posted it.
The status on Facebook was posted just minutes before the deadly attack was carried out at the San Bernardino County Health Public Health Department.
The FBI said they are now investigating the attack as an act of terrorism.
The discovery was made after police seized the couple’s electronics for examination to determine whether the couple had links to any terror groups.
Officials have added that the attack in California may have been inspired by ISIS – also known as Daesh – but there is no evidence yet to suggest the attacked was directed by the terror group.
The finding, if confirmed, could be a “game changer”, investigators said.
A FBI spokesman urged people to go about their daily lives and to not let the attack spark “mass hysteria”.
The local sheriff said there is no reason to fear a second attack, but asked residents have been urged to “remain vigilant”.
The FBI said they “are not aware” of any further threats to the US at this time and that authorities will do their best to protect American citizens.
Farook, 27, visited Saudi Arabia in the summer of 2014, the Saudi Embassy in Washington confirmed.
Christian Nwadike, who worked with Farook for five years, said his co-worker had been different since he returned from Saudi Arabia.
He said: “I think he married a terrorist.”
Malik, originally from Saudi Arabia, was not on any Saudi law enforcement or terrorism watch list, according to a source close to the Saudi government.
US officials said Farook and Malik had destroyed hard drives and other electronic devices before carrying out the mass shooting.
Officials have said no evidence has been found so far at their house so far to suggest the attack was inspired or led by ISIS.
The pair had more than 6,000 rounds of ammunition and a dozen pipe bombs on them and elsewhere, authorities said.
Farouk, a US citizen born in Illinois, was the son of Pakistani immigrants, said Hussam Ayloush, the head of a local American-Islamic Relations group.
In a press conference US President Barack Obama said it is possible the mass shooting was “terror-related” but the motive is not yet clear.
Law enforcement sources have said Farook was radicalised and was in contact with an individual under FBI investigation for terrorism links but other motives may have played a role in the shooting.
Farook attended a Christmas party with colleagues at the San Bernardino County Health Public Health Department but had left in an “angry” state, according to witnesses.
He was next seen by his co-workers dressed in battle gear and wielding an assault rifle.
The suspects killed at least 14 people and injured another 17.
Police seized flash drivers, computers and mobile phones in a raid of a townhouse in nearby Redlands believed to be used by Farook and Malik.
ISIS has called on its members around the world to strike targets in the West.
Daesh claimed responsibility for the massacres in Paris that killed 130 people and injured hundreds more on November 13.