U.S. officials appear to be on alert for retaliation from Iran after striking the country’s nuclear facilities on Saturday. Donald Trump’s administration is especially concerned about Iranian sleeper cells, also known as terrorists who could plan attacks from within the U.S., NewsNation reported.

“Intelligence services in the U.S. are working overtime to contend and mitigate risks and threats that can emerge on its domestic soil. The more protracted this conflict goes on, the heightened risk for both U.S. forces and assets in the Middle East, but also to U.S. security domestically,” Barak Seener, a senior fellow at the Henry Jackson Society, told NewsNation.

What are sleeper cells composed of?

Sleeper cells could be comprised of people living in the U.S. who are quietly living normal lives while preparing to commit acts of terrorism at any moment. Per The Independent, U.S. officials said the FBI is monitoring these threats closely as the country’s tension with Iran continues to escalate. The officials say Iran could activate the sleeper cells at any moment amid the conflict.

American citizens and many others around the world became highly concerned about the possible consequences of the conflict on Saturday when Trump claimed that the U.S. “totally obliterated” Iran’s nuclear sites of Fordow, Natanz and Isfahan.

How long has the U.S. been concerned about sleeper cells?

The U.S. has been on alert for sleeper cells for many years. The country prepared for a possible retaliation in 2020 after Trump ordered the assassination of Iranian General Qasem Soleimani. In 2021, Trump’s former national security adviser John Bolton was given Secret Service protection after several alleged sleeper cell terrorists were charged with plotting to kill him and Iranian American journalist Masih Alinejad. The two Americans have been outspoken critics of the Iranian government, CBS News reported.