The United States has begun preparing on Friday, for what could be an imminent Iranian attack on Israeli soil, and has warned the Islamic Republic to refrain from engaging in such an act. 

US President Joe Biden said he was expecting Iran to attempt to strike Israel in the short term in retaliation for a strike in Syria but warned it not to attack.

“I don’t want to get into secure information, but my expectation is sooner than later,” Biden told reporters after an event. Asked what his message was to Iran on striking Israel, Biden said, “Don’t.”

“We are devoted to the defense of Israel, we will support Israel, we will help defend Israel and Iran will not succeed,” he said.

Iran has vowed retaliation, blaming Israel for a strike on April 1 that leveled an Iranian diplomatic building in Damascus, killing seven members of the elite Revolutionary Guards, including two generals.

Biden said that Iran was “threatening to launch a significant attack” and sent the head of US Central Command, General Michael Kurilla, to Israel for urgent talks.

The White House said that the threat from Iran remained “real.”

“We are moving additional assets to the region to bolster regional deterrence efforts and increase force protection for US forces,” a Pentagon official said.

France warned its nationals against travelling to Iran, Israel, Lebanon, or the Palestinian territories, after the US embassy in Israel announced it was restricting the movements of its diplomats over security fears.

German airline Lufthansa said its planes would no longer use Iranian airspace as it extended a suspension of flights to and from Tehran.