Iran and its proxies could target the U.S. with attacks in response to the Saturday killing of Iranian Supreme Leader Ali Khamenei by Israeli and U.S. strikes, according to a U.S. intelligence assessment reviewed by Reuters.

The Saturday threat assessment produced by the Office of Intelligence and Analysis at the Department of Homeland Security said Iran and its proxies "probably" pose a threat of targeted attacks on the United States, although a large-scale physical attack was unlikely.

The report added that in the short term the main concern was that Iran-aligned "hacktivists" would conduct low-level cyberattacks against U.S. networks, such as website defacements and distributed denial-of-service attacks.

"Although a large-scale physical attack is unlikely, Iran and its proxies probably pose a persistent threat of targeted attacks in the Homeland, and will almost certainly escalate retaliatory actions — or calls to action - if reports of the Ayatollah's death are confirmed," the DHS report reviewed by Reuters said.

DHS did not immediately respond to a request for comment.

Iran on Sunday confirmed reports of Supreme Leader Khamenei's death in a strike on Saturday that was initially announced by Israel and President Donald Trump.

The DHS assessment also said Iran would probably continue its attacks against U.S. and allied targets in the Middle East and would almost certainly blame senior U.S. government officials for any protests that begin because of Trump's statement calling for regime change.

The U.S. and Israeli air war against Iran launched on Saturday widened on Monday as Israel attacked Lebanon in response to strikes by Hezbollah and Tehran kept up its missile and drone attacks on Gulf states that host U.S. military bases.

On Monday, authorities investigating a shooting on Sunday at a bar in Austin, Texas, that killed at least two people said it was too early to say if the gunman was motivated by the war in Iran.

The body of the gunman, who was killed by police, was seen in a photo obtained by Reuters wearing a shirt with an Iranian flag and “IRAN” spelled out in green, white and red across the front. He was also wearing a sweatshirt that said "Property of Allah" on it, a U.S. law enforcement official told Reuters.