The FBI has ramped up surveillance of individuals believed to have ties to Iran-backed terror groups operating in the United States, according to a senior law enforcement official. The move comes as President Donald Trump weighs whether to involve the U.S. military in the ongoing hostilities between Israel and Iran.

CBS News reported that the surveillance effort includes tracking potential Hezbollah sleeper cells. The Lebanon-based group, which receives backing from Tehran, has been warned by Israeli Defense Minister Israel Katz not to escalate the conflict by joining in.

The increased security measures follow recent claims from Israeli Prime Minister Benjamin Netanyahu, who alleged that the Iranian regime is plotting to assassinate Trump due to his hardline stance on Iran’s nuclear ambitions.

“They want to kill him. He’s enemy No. 1,” Netanyahu told Fox News’ Bret Baier during an interview on Sunday. “He’s a decisive leader. He never took the path that others took to try to bargain with them… giving them basically a pathway to enrich uranium, which means a pathway to the bomb, padding it with billions and billions of dollars.”

Trump, who has called for Iran’s “unconditional surrender,” has not yet decided whether the U.S. will become directly involved in the conflict. White House Press Secretary Karoline Leavitt said Thursday that a decision is expected within two weeks.

Meanwhile, the U.S. military is increasing its presence in the region. A U.S. official confirmed Friday that the USS Nimitz, which left the South China Sea earlier this week, is set to arrive in the Middle East this weekend. It will join the USS Carl Vinson, which is already operating in the area—placing two aircraft carriers in the region simultaneously.

The prospect of deeper U.S. involvement in the Middle East has triggered mixed reactions from lawmakers. Some warn against entangling American forces in another foreign war, while others argue that assertive action is needed to deter Tehran and defend U.S. interests.