Mounting concerns about Iran ‘sleeper cells’ after 1,500 stopped at border
U.S. officials and lawmakers are raising alarms about the number of Iranian nationals who entered or attempted to enter the United States during the Biden administration, warning that the unknown number who may have crossed the border undetected could pose a serious national security risk.
According to Sen. Bill Hagerty of Tennessee, a member of the Senate Foreign Relations Committee and former U.S. ambassador to Japan during President Trump’s first administration, roughly 1,500 Iranians were stopped at the southern border during those years. What concerns officials more, he said, is that authorities cannot determine how many others may have entered the country without being intercepted.
Hagerty pointed to reports indicating that about half of those detained were later released into the United States while awaiting court proceedings. A Fox News report previously stated that 1,504 Iranian nationals were arrested at the border between 2021 and 2024, with around 700 allowed to remain in the country pending immigration hearings.
The United States has long designated Iran as a state sponsor of terrorism, which has intensified concerns among lawmakers about the potential security implications.
Data cited by the Niskanen Center and drawn from Customs and Border Protection records indicates the number of Iranians encountered at the border increased to about 1,650 between 2022 and 2025. Officials noted that many travelers from Iran had passed through São Paulo, Brazil, which authorities have described as a major center for passport fraud.
The issue gained additional attention after federal agencies circulated a security bulletin warning that Iran could attempt to activate “prepositioned sleeper assets.” The alert came as Iran’s leadership has suffered significant losses following ongoing U.S. and Israeli military strikes.
The possibility of retaliation on American soil has heightened concerns in Washington. Iran has continued attacks in the Gulf region, and retaliatory actions have resulted in the deaths of at least 13 U.S. service members.
President Trump addressed the issue on March 11, criticizing the previous administration’s border policies and saying authorities are monitoring many of the individuals who entered the country.
Security worries were further intensified after a series of violent incidents in the United States. In Michigan, a Lebanese American man drove a vehicle containing explosives into a synagogue in West Bloomfield. In Virginia, a gunman with alleged ISIS connections opened fire at Old Dominion University, killing an ROTC instructor.
Amid these developments, FBI Director Kash Patel and CIA Director John Ratcliffe met with Republican senators at the Capitol to discuss the upcoming expiration of federal surveillance authorities and the broader national security environment.
Hagerty warned that officials cannot account for everyone who may have entered the country illegally. He said the possibility that sleeper cells could already be operating in the United States cannot be ruled out.
Other lawmakers echoed those concerns. Sen. Ron Wyden of Oregon, the vice chair of the Senate Intelligence Committee, said the country is facing a period of significant security challenges, though he noted he could not discuss classified information.
Sen. James Risch of Idaho, another member of the intelligence panel, said the situation requires continued vigilance.
Sen. Rick Scott of Florida, who serves on the Homeland Security Committee, said the threat should not be underestimated, emphasizing that it would only take one individual to carry out a devastating attack.
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