San Bernardino, CA, shooter Syed Rizwan Farook had contact with people from at least two terrorist organizations overseas, including the Al Qaeda-affiliated Nusra Front in Syria, a federal law enforcement official said Friday.

His wife and fellow shooter, Tashfeen Malik, also pledged allegiance to an Islamic State leader in a Facebook posting, two federal law enforcement officials said.

The revelations came as the FBI formally announced it was investigating the shooting rampage as an act of terrorism, reports the Los Angeles Times .

FBI Director James Comey said the assailants showed signs of "radicalization" but that there was no evidence they were part of a larger terrorist network.

Farook and Malik died in a police shootout Wednesday, several hours after bursting into a holiday potluck for the San Bernardino County Health Department and killing 14 people.

As the investigation expands, the law enforcement source said, agents are trying to learn more about the couple's contacts in the U.S. and overseas, "especially those in Pakistan," where Farook visited and Malik was born.

One key question, said the official, "is if they had any weapons or terror training in Pakistan." The source described "some kind" of contact between Farook and people from the Nusra Front and the radical Shabab group in Somalia. It's unclear what type of contact or with whom.