The U.S. is moving extra defense "assets" into place in the Mideast before an expected attack on Israel by Iran, according to officials.
"We are moving additional assets to the region to bolster regional deterrence efforts and increase force protection for U.S. forces," said a U.S.defense official in Washington, Barron's and other media reported.
The U.S. embassy said earlier that staff had been told not to travel outside the greater Jerusalem, Tel Aviv or Beersheba areas "out of an abundance of caution."
Iran is expected to launch an attack on Israel as soon as Friday night or Saturday in retaliation for an attack on Syria 11 days ago that killed 13 people. Israel has not claimed responsibility for the assault on Syria.
President Biden noted on Wednesday that Iran was threatening to launch a "significant attack," and he vowed to offer "ironclad" support to Israel.
Israeli Prime Minister Benjamin Netanyahu said his government was ready to meet any challenge, and warned that Israel would harm any country that caused it harm.