"I don't want to get into secure information but my expectation is sooner than later," Biden said to reporters on Friday when asked how imminent an Iranian attack on Israel would be, CNN reported.

Asked what his message to Iran is right now, the President said, "Don't."

In response to more shouted questions from reporters in the room, asking if American troops were at risk -- Biden returned to the podium and said that the US is "devoted" to the defence of Israel.

"We are devoted to the defence of Israel. We will support Israel, we will help defend Israel and Iran will not succeed," Biden said.

The US has been on high alert for a significant Iranian retaliatory attack on Israel in recent days as fears grow of a wider regional war, CNN reported.

There remains a "real," "credible" and "viable" threat of Iran launching strikes, the White House said on Friday, following Israel's attack on an Iranian diplomatic compound in Syria last week that killed three Iranian generals.

Biden, who warned this week that Iran was threatening a "significant attack" on Israel, has been receiving constant updates on the situation from his national security team.

The US and several other countries, including Britain and France, issued new travel guidelines for government employees in Israel as the Iranian threat loomed.

"We're watching this very, very closely," said John Kirby, the National Security Council spokesman, who declined to provide information about the expected timing of the threat.

The US will attempt to intercept any weapons launched at Israel if it's feasible to do so, two US officials told CNN, an indication of the level of ongoing cooperation between the two militaries.

US Navy forces in the Red Sea have previously intercepted long-range missiles launched from the Houthis in Yemen towards Israel. US forces in Iraq and Syria could also potentially intercept drones and rockets targeting northern Israel, depending on the location from which they're launched, CNN reported.

The Defence Department is also moving additional assets to the Middle East region "to bolster regional deterrence efforts and increase force protection for US forces," a US Defence official told CNN, as Israel and the US brace for a potential Iranian attack.

The Pentagon has been working specifically to bolster air defences for the US troops stationed in Iraq and Syria who came under attack by Iran-backed proxy forces over 100 times between October and February. In January, three US service members were killed when a drone got through US air defences at the Tower 22 base in Jordan.

The US is not anticipating that Iran or its proxies will attack US forces as part of its retaliation but is moving the assets just in case.

"It would be imprudent if we didn't take a look at our own posture in the region to make sure that we're properly prepared," Kirby added.

CNN reported last week that the US was on high alert and actively preparing for an attack by Iran targeting Israeli or American assets in the region. Officials said such an attack could come within the week.

CNN reported earlier this week that an Iranian attack on Israel would likely be carried out by Iranian proxy forces in the region rather than by Iran directly, according to two people familiar with US intelligence on the matter.

Tehran is wary of a dramatic escalation in the fighting, the sources said, and does not want to give the US or its allies an excuse to attack Iran directly.

The sources said Iran and its proxy militia groups do not appear poised to attack US troops or other assets in the region, but they noted that Iran does not have perfect command and control over all its proxy forces, so the possibility of an attack on US assets cannot be completely ruled out, CNN reported.

The sources told CNN that US intelligence assesses that Iran has urged several of its proxy militia groups to simultaneously launch a large-scale attack against Israel, using drones and missiles, and that they could attack as soon as this week.

"The threat is very clear and credible," said one of the sources.

"They have put the pieces in place to conduct the attack now. Just waiting for the right time."

Biden spoke with his Israeli counterpart, Prime Minister Benjamin Netanyahu, about the threat of an Iranian attack during a telephone call last week.

A direct strike on Israel by Iran is one of the worst-case scenarios 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 Biden has long sought to avoid, CNN reported.

Biden is receiving briefings multiple times a day on the situation, Kirby said.

He added on Friday that US officials were in "constant communication" with their Israeli counterparts about the matter and that steps were underway to ensure Israel is able to defend itself.

"We are certainly mindful of a very public and what we consider to be a very credible threat made by Iran in terms of potential attacks on Israel," Kirby said on Friday.

He pointed to a visit to Israel on Friday by US Central Command Chief General Erik Kurilla to have "those conversations directly with his IDF counterparts".

Kurilla's trip to Israel was moved up because of the expectation of an Iranian response to Israel's targeting of the Iranian consulate in Damascus, Syria, last week, CNN reported.

There have also been a number of conversations in which US officials have urged Israel not to escalate the situation in retaliating against Iran, according to one of the US officials said.

Separately, US officials were frustrated with their Israeli counterparts over the lack of information Israel shared prior to carrying out the strike in Damascus last week, sources told CNN.

Israel only informed a US official when its planes were already in the air en route to Syria, another US official said.

"We were not aware that Israel was going to carry out this airstrike in advance," the official added.

"Minutes before it happened and when Israeli planes were already in the air, Israel reached out to a US official to say they were in the process of conducting a strike in Syria. It did not include any details on who they were targeting or where it would be conducted, and the strike was already underway before word could be passed through the US government."

US Secretary of State Antony Blinken spoke with the Foreign Ministers of Turkey, China and Saudi Arabia to urge them to press Iran not to escalate the conflict in the Middle East after threats made by Iran against Israel, State Department Spokesperson Matthew Miller said on Thursday.

Miller added that the US has also "engaged with European allies and partners over the past few days" to deliver a similar message on Iran. German Foreign Minister Annalena Baerbock and British Foreign Secretary David Cameron have both spoken to the Iranian Foreign Minister in recent days.

Blinken "has been making clear to every country that has any semblance of a relationship with Iran that it is in their interest to use that relationship to send a message to Iran that they should not escalate this conflict. But I will let those countries speak for themselves about what action they may or may not take," Miller said.

The US State Department has restricted the travel of US government personnel in Israel in the wake of public threats against Israel by Iran, CNN reported.

"Out of an abundance of caution, US government employees and their family members are restricted from personal travel outside the greater Tel Aviv (including Herzliya, Netanya, and Even Yehuda), Jerusalem, and Be'er Sheva areas until further notice," a security alert posted by the US Embassy on Thursday said, "US government personnel are authorised to transit between these three areas for personal travel."

"The security environment remains complex and can change quickly depending on the political situation and recent events," the alert noted.

France has advised its citizens to "absolutely refrain" from travelling to Iran, Lebanon, Israel and the occupied Palestinian territories due to the risk of "military escalation," the French Foreign Ministry said on Friday.

The Ministry added that families of diplomatic staff in the Iranian capital Tehran will be returned to France and civil servants will be banned from work missions to those countries and territories.

The French Foreign Minister Stephane Sejourne issued the new recommendation following a crisis meeting on the region, the Ministry said in a post on X.