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

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, including CNN’s MJ Lee asking if American troops were at risk – Biden returned to the podium and said that the United States is “devoted” to the defense of Israel.

“We are devoted to the defense 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.

There remains a “real,” “credible” and “viable” threat of Iran launching strikes, the White House said 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 Defense Department is moving additional assets to the Middle East region “to bolster regional deterrence efforts and increase force protection for US forces,” a US defense official told CNN, as Israel and the US brace for a potential Iranian attack.

The Pentagon has been working specifically to bolster air defenses 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 servicemembers were killed when a drone got through US air defenses 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 said.