The Pentagon is beefing up its presence in the Middle East, U.S. officials said Friday, assigning additional warships and aircraft amid heightened concern about an imminent Iranian strike on Israel and worries of spillover violence intended at American personnel.

“We are moving additional assets to the region to bolster regional deterrence efforts and increase force protection for U.S. forces,” one defense official said, speaking on the condition of anonymity to discuss sensitive and ongoing military movements.

The shift highlights the Biden administration’s anxiety that U.S. support of Israel amid the Gaza war could fuel greater violence in the Middle East, even as officials in Washington have disavowed American involvement in an April 1 assault in Damascus that killed two Iranian military officers. Tehran has blamed Israel for the attack and pledged to react.

Another U.S. defense official familiar with the Pentagon’s plans declined to specify which warships or aircraft are engaged, citing security concerns.

Other warships that have been deployed in the region, including the aircraft carrier USS Dwight D. Eisenhower and the destroyers USS Carney and USS Arleigh Burke, remain nearby, this individual said.

U.S. officials have not stated whether the anticipated reprisal would come from Iran directly or from an Iran-backed entity.

President Biden, in answer to questions from reporters Friday afternoon regarding the timing of a potential attack by Iran or its proxies, said his “expectation” was that the attack would happen “sooner than later.” Asked what his message was to Iran, he replied, “Don’t.”

Senior Pentagon leaders were frustrated that Israel did not tell the U.S. authorities ahead of the Damascus strike. Officials told The Washington Post last week that Defense Secretary Lloyd Austin spoke personally to his Israeli counterpart, Defense Minister Yoav Gallant, and highlighted the ramifications for U.S. soldiers and interests in the region.

While Iran has declared it holds the United States responsible for Israeli actions, including the raid on its plant in Damascus, it is not obvious whether Tehran would attempt to take action against the United States directly in response or focus entirely on Israel.