PresidentDonald Trumpsaid the administration is "on top of" possible Iranian sleeper cells operating inside the United States, offering few details about their existence and level of potential threat.
At a press conference on Monday, March 9, Trump responded to a question about whether the Iranian government had activated undercover groups, or cells, located within the country.
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"They've been trying for a long time, and we've been very much on top of it," Trump said.
"We're watching every single one of them, yeah. We know a lot about them," the president added. He alleged the Democrat-led shutdown of the Department of Homeland Security was impeding his administration's efforts to address such concerns.
Smoke rises following an explosion, after Israel and the U.S. launched strikes on Iran, in Tehran, Iran, February 28, 2026." style="max-width:100%; height:auto; border-radius:6px; margin:10px 0;" loading="lazy" /> 
Smoke rises following an explosion after the U.S. and Israel reportedly launched an attack against Iran, in Tehran, Iran, February 28, 2026, in this screen grab taken from video." style="max-width:100%; height:auto; border-radius:6px; margin:10px 0;" loading="lazy" /> 
A plume of smoke rises following a reported explosion in Tehran on February 28, 2026. Two loud blasts were heard in Tehran on February 28 morning by AFP journalists, and two plumes of thick smoke were seen over the centre and east of the Iranian capital. Israel's defence ministry announced it had launched a "preemptive strike" on Iran as sirens sounded in Jerusalem and people across the country received phone alerts about an "extremely serious" threat." style="max-width:100%; height:auto; border-radius:6px; margin:10px 0;" loading="lazy" />
U.S. President Donald Trump pumps his fist after disembarking Air Force One at Palm Beach International Airport in West Palm Beach, Florida, U.S., February 27, 2026. Hours later, Trump made live comments about the military strikes he launched against Iran." style="max-width:100%; height:auto; border-radius:6px; margin:10px 0;" loading="lazy" /> 
Buildings inin Tehran stand after Israel and the U.S. launched strikes on Iran, February 28, 2026." style="max-width:100%; height:auto; border-radius:6px; margin:10px 0;" loading="lazy" /> 
Latest photos capture US and Israeli strikes against Iran
Smoke rises following an explosion,after Israel and the U.S. launched strikes on Iran, in Tehran, Iran, February 28, 2026.
The FBI is thelead agencyfor investigating and preventing acts of domestic and international terrorism. The funding lapse for the Department of Homeland Security has primarily affected FEMA, the Transportation Security Administration and Customs and Border Protection. However, much of Homeland Security'stypical work, including ICE operations, continues.
The Department of Homeland Security did not immediately respond to requests for comment. When asked about Trump's remarks about sleeper cells, the FBI said it had no comment.
ABC todayreportedthe United States has intercepted encrypted communications believed to have originated in Iran that may serve as "an operational trigger" for "sleeper assets" outside the country, according to the news outlet's review of a federal government alert sent to law enforcement agencies.
What is a sleeper cell?
A sleeper cell refers to a group of operatives who are working undercover until activated inside enemy territory. It can refer to a spy network or terrorist group.
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The administration has not released any advisory about specific threats of Iranian or Iran-aligned sleeper cells in the United States since the U.S.-Israel war with Iran began on Feb. 28.
However, the FBI and the Department of Homeland Security are on a war footing, USA TODAY has reported, andhad already been in that status in thelead-up to the U.S. and Israel-launched strikes. The United States wenton high alertlast June overconcerns of retaliationfrom Tehran, after the United States and Israel bombedthree Iranian nuclear sitesduring the 12-day war.
The Iranian regime has a long history –dating back at least 46 years– of assassinations and other terrorist plots on U.S. soil and against Americans overseas.
Those include plots the United States has disrupted against Iranian dissidents, andagainst Trumpand his former National SecurityAdviser, John Bolton, in response to a 2020 military strike that killed Iranian military leaderGen. Qassem Soleimani.
On March 6, a federal juryconvicted an Iranian operative, Asif Raza Merchant, of taking part in a terrorism attempt andplot to assassinateTrump in 2024, well before the war in Iran.
Contributing: Josh Meyer, USA TODAY.
Kathryn Palmer is a politics reporter for USA TODAY. You can reach her atkapalmer@usatoday.comand on X @KathrynPlmr. Sign up for her daily politics newsletterhere.
This article originally appeared on USA TODAY:US is monitoring possible Iran sleeper cells. What are they?