The US intelligence community has issued a flurry of private warnings in the past week to American companies and government agencies urging vigilance and the hardening of possible targets of cyber attack by the Iranian regime in response to the war with Tehran, according to national security sources and memos reviewed by CNN.

While no specific or credible threat has been outlined, in one recent bulletin to US law enforcement agencies, the Department of Homeland Security warned of a heightened threat environment following the killing of Iran’s supreme leader, Ayatollah Ali Khamenei.

U.S. intelligence officials routinely send bulletins to law enforcement agencies across the country, sharing information on potential threats and best practices for protecting the public.

Citing open-source intelligence, the DHS “critical incident note” said that “two top Iranian religious leaders issued separate Farsi-language fatwas calling on Muslims worldwide to take revenge for the killing” of Khamenei.

“The fatwas, Iranian government rhetoric, and online messaging from regime supporters promoting retaliation against the US heightens the threat from violent extremists who support the Iranian regime,” the bulletin said.

The bulletin also referenced a decree from the Iranian Revolutionary Guard Corps, which indicated “the enemy … will no longer have security anywhere in the world, even in their own homes.”

U.S. officials have not announced any known credible threats to the homeland, but a law enforcement source familiar with the situation previously told CNN the FBI went on an elevated alert status across the country following the launch of strikes by US and Israel. Authorities were particularly concerned about enhancing security measures around US energy infrastructure, hardening potential government targets against cyber threats from sophisticated Iranian actors, and securing the border.

In a separate recent bulletin to private companies, U.S. security officials warned:

“Ongoing claims and calls for cyber attacks targeting US entities by Iranian-aligned groups could lead to an increase in malicious activity against the financial services sector,” adding that “historically, the US financial sector has been viewed as a priority target and a target of opportunity by Iranian-aligned cyber actors.”

The bulletin listed numerous recent public claims of responsibility by Iranian-affiliated hackers targeting the cyber infrastructure of Israel and allied nations.

“Although these claims are unverified,” the bulletin read, “organizations are advised to continue to be vigilant and monitor for any potential incoming threat actor targeting.”

In another recent notice to U.S. defense contractors, the FBI and National Security Agency warned that “Iranian-affiliated cyber actors may target US devices and networks for near-term cyber operations,” noting that defense-related companies, “particularly those possessing holdings or relationships with Israeli research and defense firms, are at an increased risk.” (CNN)

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