Saudi Arabia has focused on an attack using armed drones that targeted oil-pumping stations in the country.
State Department officials said threats in the region were credible and based on intelligence showing Iranian-backed militias had been moving personnel and weaponry as well as stepping up surveillance of USA and US -affiliated facilities in Iraq and other parts of the Middle East.
"Ensuring the safety of US Government personnel and citizens is our highest priority ... and we want to reduce the risk of harm", a State Department spokesman said.
This contradicts U.S. intelligence that led the Trump administration to both deploy additional military to the Persian Gulf and order U.S. Embassy personnel in Iraq to vacate amid the Iranian tensions.
Mr Trump's administration has pursued a policy of "maximum pressure" against Iran, including tightening economic sanctions, since withdrawing the USA from a deal created to limit Iran's nuclear program past year.
Iranian-backed proxy forces have been operating in Iraq and other Middle Eastern nations for years, according to U.S. officials.
"This moment in history, because the enemy has stepped into the field of confrontation with us with all the possible capacity, is the most decisive moment of the Islamic revolution", said Major General Hossein Salami.
The United Arab Emirates, a key U.S. ally in the region, has even said it is committed to a "de-escalation" with Iran. Netanyahu made his plea Tuesday, during an event marking the one-year anniversary of Israel's U.S. Embassy moving to Jerusalem.
A helicopter carrying U.S. Secretary of State Mike Pompeo is seen taking off from Baghdad International Airport last week. "If the threat level seems to go up then we'll raise our force protection measures accordingly".
Helicopters took off throughout the day from the vast embassy compound near the Tigris River, carrying staff out, according to an Iraqi source and a diplomatic source inside Baghdad's fortified Green Zone. A USA official told Reuters late on Wednesday that the evacuation was complete.
The remarks contradict comments from Maj Gen Chris Ghika, a British senior officer in the US-backed coalition fighting Islamic State, who said: "There's been no increased threat from Iranian-backed forces in Iraq and Syria".
It was unclear how many were affected, and there was no word on any specific threat.
Germany and the Netherlands have halted all training missions in Iraq as tensions continue to rise between the U.S. and Iran, which supports proxy militias there.
France has no plans at this point to suspend military training activities in Iraq, Reuters reported a source close to the French Defense Ministry as saying on Wednesday.
"They have no business declaring a war without the consent of Congress", she said.
Talking more about USA military action against Iran under the pretext of allegations that Iran is preparing strikes against U.S. forces in the Middle East, the article said: "The United States is poorly prepared for another conflict in the region; it has the support of none of its North Atlantic Treaty Organisation allies, not even - as Mr. Hunt made clear - Britain".
Iraqi Prime Minister Adel Abdul Mahdi said on Tuesday he was getting indications from talks with both the United States and Iran that "things will end well" despite the rhetoric.