"As of today, and based on the information and the facts as we know them, we are now investigating these horrific acts as an act of terrorism," said David Bowdich, assistant director of the Los Angeles FBI office.
The FBI has uncovered evidence of extensive planning, Bowdich said. Authorities have discovered some phone connections between at least one of the San Bernardino shooters and others being investigated by federal officials, Bowdich said. He added that a number of pieces of evidence pushed authorities to launch a terrorism investigation.
No one is under arrest in connection with Wednesday's San Bernardino massacre, Bowdich said. Bowdich did not rule out some arrests happening in the future. The man and woman who police say were the attackers were killed by police on Wednesday.
Bowdich said his agency had no information about any credible terrorist threats anywhere in the United States.
This developing story will be updated.