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Israel is bracing for a direct and unprecedented attack by Iran on government targets as soon as Saturday, according to people familiar with Western intelligence assessments, a move that has the potential to trigger an all-out regional war.

An assault from Iranian soil has emerged as one of the main scenarios expected by the Jewish state and its allies, said the people, who asked not to be identified as they aren't authorized to discuss the matter publicly. A bombardment with drones and precision missiles could come within the next 48 hours, they said.

The U.S. is preparing defenses and moved additional military assets to the region, while intensifying diplomatic efforts to rein in hostilities, the people said. The attack still hasn't been approved by Tehran's highest-ranking officials, they said.

An Iranian missile and drone barrage would represent a retaliation for a deadly strike on its diplomatic compound in Syria last week, which the Islamic Republic blames on Israel. Supreme Leader Ayatollah Ali Khamenei has repeatedly said Israel will be "punished" for the assault, though stopped short of saying what form such a counter move would take.

One of the people said it's possible that the increasingly inflammatory rhetoric between Israel, Iran and the U.S. could be grandstanding, but said the working assumption for Israel and allies is that an attack is imminent. Diplomatic back-channels are in overdrive, the people said.

U.S. officials including Jake Sullivan and Brett McGurk have been working to send messages to Iran, including through an established Swiss channel, one of the people said, while talking to Israel, Saudi Arabia, Qatar and other governments.

White House spokeswoman Karine Jean-Pierre said Thursday the U.S. has warned Iran not to use Israel's attack on Syria as a pretext to escalate hostilities further.

"We've seen the threats coming from Iran and so we have made ourselves very clear where we stand in supporting Israel's security," she said. "That is ironclad."

Any Iranian attack on Israel would likely be a combination of missiles and drones, based on current capabilities outlined in a new Defense Intelligence Agency Worldwide Threat assessment released late Thursday.

The regime "has a substantial inventory of ballistic and cruise missiles capable of striking targets as far as 2,000 kilometers from its borders," the agency said.

Bloomberg News reported on Wednesday the U.S. and allies were expecting a major escalation of hostilities, with targeted attacks on Israeli government and military sites. The Jewish state hasn't claimed or denied responsibility for the Damascus attack, in keeping with a decades-long policy of ambiguity on operations in Syria, Lebanon and elsewhere.

A direct Israel-Iran conflict would significantly ratchet up hostilities in the Middle East, where tensions have been rising since Israel began its war against Hamas in Gaza in October, after the Iran-backed militant group invaded the country and killed about 1,200 people. Hamas is designated a terrorist organization by the U.S. and European Union.

Other members of the Islamic Republic's so-called Axis of Resistance, chiefly Hezbollah in Lebanon and the Yemen-based Houthis, have stepped up their aggression in recent months.

The escalating hostilities have drawn direct intervention from senior diplomats. U.K. Foreign Secretary David Cameron warned Iran Thursday that an attack would escalate and drag in a wider array of actors.

Western officials said intelligence showed Iran is preparing an attack on Israel any day after Eid al-Fitr, the Muslim holiday celebrated on April 10, adding the next 48 hours were critical to see if the message to diffuse tensions had successfully reached Tehran.

With assistance from Alberto Nardelli and Tony Capaccio.