American intelligence analysts and officials said on Friday that they expected Iran to strike multiple targets inside Israel within the next few days in retaliation for an Israeli bombing in the Syrian capital on April 1 that killed several senior Iranian commanders.

The United States, Israel’s pre-eminent ally, has military forces in several places across the Middle East. But Iran is not expected to target them in order to avoid a direct conflict with the United States, according to U.S. and Iranian officials who spoke anonymously about the expected attacks, which they were not authorized to discuss publicly.

Any Iranian strike inside Israel would be a watershed moment in the decades of hostilities between the two nations that would most likely open a volatile new chapter in the region. Israel and Iran do not maintain any direct channels of communication, making the chances far greater that each side could misread the other’s intentions. And an Iranian attack would heighten the risk of a wider conflict that could drag in multiple countries, including the United States.

In remarks to reporters on Friday, President Biden said that he expected a military attack against Israel “sooner than later,” and that his message to Iran was “don’t.”

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

In anticipation of an Iranian strike, several countries, including the United States, have issued new guidelines to their citizens for travel in Israel and the surrounding region. The Israeli military said its forces were on high alert.