President Barack Obama says U.S. must remain vigilant against terror threats

In his annual year-end news conference Friday, U.S. President Barack Obama asked Americans to remain vigilant as he sought to assure them that his administration was working overtime to keep them safe by "squeezing" the heart of Islamic State overseas.

"We're going to defeat ISIS and we're going to do so by systematically squeezing them, cutting off their supply lines, cutting off their financing, taking out their leadership, taking out their forces, taking out their infrastructure," Obama told reporters.

He said the U.S. will continue to hit ISIS "harder than ever" next year.

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Obama said Americans must also "remain vigilant here at home."

"All of us can do our part by staying vigilant, by saying something if we see something that is suspicious, by refusing to be terrorized and by staying united as one American family."

Obama said ISIS's capacity to infiltrate Western countries, especially through social media, will continue to make the militant group dangerous for "quite some time."

When asked about visa reviews for people coming into the U.S., Obama stressed that no government can read ever single social media post, email or text message, and that it is important to distinguish between public social media posts versus private messages.

​After the news conference, Obama was to depart for San Bernardino, Calif., where he planned to meet with families of the 14 victims of the recent mass shooting.

Addressing the shooting, Obama said intelligence can't always catch terror plots ahead of time and that lone wolf attacks are a different kind of challenge.

Closing Guantanamo 

Obama said the U.S. is working systematically to reduce the population at the Guantanamo Bay prison and that the administration will attempt to work with Congress to close the facility.

"We will continue to steadily chip away at the population," Obama said, noting that by early 2016 the administration expects the prison population will be below 100.

Obama said it's really expensive to detain "a handful of people" at Guantanamo, which costs several million dollars per person, and that the facility continues to be a magnet for jihadi recruitment. 

Obama said his administration will attempt to get Congress to back a plan to close the facility before he considers whether to use his executive authority to address the issue.