The 66-year-old father of California jihadist Syed Rizwan Farook was placed on the FBI’s terrorist watch list as investigators expanded their probe to include the killer’s family members and friends, federal law enforcement sources said Monday.

Farook’s dad, who is also named Syed, is being monitored by the FBI because of his son’s terrorist status and his own trips to Pakistan.

The elder Farook came to the United States in 1972 and became a US citizen in 1999.

“Farook, although he is dead, is now officially listed by the FBI as a terrorist,” a federal law enforcement source told The Post. “His father is watch-listed because of his close association to Farook and his extensive ties to Pakistan.”

After the massacre, the elder Farook tried to distance himself from his son, telling reporters, “His views were conservative. My views were liberal.”

Authorities also are investigating whether Farook’s mom, Rafia, knew about her son’s plot and stockpile of weapons before he and his wife, Tashfeen Malik, killed 14 people in San Bernardino.

“The mom definitely has exposure as a potential co-conspirator,” a law enforcement source said. “We are trying to uncover any evidence of her possible involvement which could lead to charges.”

Another US official briefed on the matter said that people who knew Farook and Malik observed the couple change — but never reported their suspicions to law enforcement.

“There were people within their circle who saw them change — Farook especially — and no one said a word to the authorities,” the source said.

“This is of great concern to us. We need people to come forward and tell us when there is a change like this so we can do something.”

Meanwhile, Farook’s family issued an apology for his evil deeds, just a few days after their lawyers insisted Malik was nothing but a “caring housewife.”

“The Farook family would like to extend their deepest sympathies and condolences to the families, friends, and colleagues of the victims in Wednesday afternoon’s horrific event at the Inland Regional Center in San Bernardino, California,” the statement reads.

“We have cooperated with law enforcement and will continue to do so,” the statement continues.

“We understand there are many questions that need to be answered but right now, our hope and prayer is for peace and healing for the victims, their families, friends, and colleagues, the entire community of San Bernardino, and those touched by these events throughout the state of California and our nation.”