WASHINGTON (CNN) — The United States is on high alert and actively preparing for a “significant” attack that could come as soon as within the next week by Iran targeting Israeli or American assets in the region in response to Monday’s Israeli strike in Damascus that killed top Iranian commanders, a senior administration official tells CNN.

Senior U.S. officials believe that an attack by Iran is “inevitable” – a view shared by their Israeli counterparts, that official said. The two governments are furiously working to get in position ahead of what is to come, as they anticipate that Iran’s attack could unfold in a number of different ways – and that both US and Israeli assets and personnel are at risk of being targeted.

A forthcoming Iranian attack was a major topic of discussion on President Joe Biden’s phone call with Israeli Prime Minister Benjamin Netanyahu on Thursday.

As of Friday, the two governments did not know when or how Iran planned to strike back, the official said.

A direct strike on Israel by Iran is one of the worst-case scenarios that the Biden administration is bracing for, as it would guarantee rapid escalation of an already tumultuous situation in the Middle East. Such a strike could lead to the Israel-Hamas war broadening into a wider, regional conflict, something which Biden has long sought to avoid.

Iran vowed to take revenge after Israel’s airstrike on Iran’s embassy complex in Syria, which killed at least seven officials. Mohammed Reza Zahedi, a top commander in Iran’s elite Revolutionary Guards (IRGC), and senior commander Mohammad Hadi Haji Rahimi were among those killed, according to Iran’s Foreign Ministry.

At least six Syrian citizens were also killed, Iranian state television reported on Tuesday.

Zahedi, a former commander of the IRGC’s ground forces and air force, and the deputy commander of its operations, is the most high-profile Iranian target killed since then-U.S. President Donald Trump ordered the assassination of IRGC Gen. Qassem Soleimani in Baghdad in 2020.

The U.S. was quick to inform Iran that the Biden administration was not involved and had no advance knowledge of Monday’s strike on the embassy and has warned Iran against coming after American assets.

“The United States had no involvement in the strike and we did not know about it ahead of time,” a National Security Council spokesperson told CNN earlier this week.

The United States considers its own embassies and consulates abroad, as well as foreign countries’ embassies and consulates in the U.S., to have a special status. According to the U.S. State Department, “an attack on an embassy is considered an attack on the country it represents.”

On Tuesday, the Pentagon’s Deputy Press Secretary Sabrina Singh said the U.S. assessment was that Israel had carried out the airstrike.

“That’s our assessment, and it’s also our assessment that there were a handful of IRGC top leaders there. I can’t confirm those identities, but that’s our initial assessment right now,” Singh said.

Israel has intensified its military campaign against Iran and its regional proxies following the Oct. 7 attack on Israel by Tehran-backed Palestinian group Hamas, which killed about 1,200 people and saw more than 200 taken hostage.

Israel’s subsequent war in Gaza has killed more than 32,800 people, according to the Ministry of Health in the besieged enclave, wrought widespread destruction and brought more than 1 million people to the brink of a man-made famine.

CNN’s Helen Regan, Hamdi Alkhshali and Tamara Qiblawi contributed to this report