WASHINGTON — Senators from both sides of the aisle demanded Wednesday that the Trump administration explain why it had evacuated U.S. diplomatic missions in Iraq and brief lawmakers on the alleged threats from Iran that prompted the move.

Sen. Bob Menendez of New Jersey, the ranking Democrat on the Senate Foreign Relations Committee, called on the administration "to immediately provide this committee with a briefing on the decision to order the departure of embassy staff, the intelligence on what Iran may be planning to do and any plans to go to war with Iran."

Speaking at a committee hearing, Menendez said there were only two reasons to evacuate the U.S. missions in Iraq: Americans working at the missions are at risk, or it is "in preparation for military action in Iran."

The senator said it was the committee's duty to help write laws to authorize the use of military force and to oversee the State Department and the safety of its employees.

"And yet the Trump administration has not provided any information to this committee on the intelligence behind their decisions and what they plan to do in Iraq or Iran," he said.

Menendez added that Congress has not authorized war with Iran and if the Trump administration was "contemplating military action with Iran, it must come to Congress to seek approval."

At the same hearing, Sen. Mitt Romney, R-Utah, said he agreed with Menendez "about the need for a classified briefing on the matters in Iraq" and that "I hope that either the entire committee or perhaps the chair and the ranking member would be able to have that kind of briefing"

The chairman of the Senate Foreign Relations Committee, Sen. Jim Risch, R-Idaho, said a full briefing for the entire Senate was "in the works."

Sen. Lindsey Graham, R-S.C., an outspoken advocate for tough action toward Iran and a frequent defender of President Donald Trump, also said the State Department and the Defense Department needed to brief lawmakers about why it had chosen to evacuate the U.S. missions in Iraq.

"I would urge the State Department and DoD to come down here and explain to us what's going on," Graham told reporters. "Because I have no idea what the threat stream is beyond what I read in the paper."

He added: "I think there are a lot of people in my shoes that are going to support standing up to Iran, but we need to understand what we're doing."

The State Department earlier Wednesday ordered the departure of nonemergency employees from the U.S. embassy in Baghdad and the U.S. consulate in the northern city of Erbil, and renewed a warning to American citizens not to travel to Iraq.

The announcement did not say how many personnel were affected, and did not offer more details about the threat posed to Americans in Iraq.

Senior State Department officials told reporters Wednesday that the ordered departure of some U.S. government personnel from Iraq was because of an "imminent threat" from Iranian proxies based on increased intelligence reporting received within the last seven days.

Asked about the seriousness of the threat, the official said "comparisons to Iraq 2003 are simply wrong. The much more appropriate analogy is Iraq 2011" when attacks were launched at U.S. installations. That was the year that the U.S. withdrew ground troops from the country.

The officials pointed to Iran affiliated groups as the source of the threat. They said the move is not about going to war with Iran, but that it would be gross negligence to not take precautions in light of credible threats.

The State Department would not specify the number of U.S. personnel in Iraq, citing security concerns. A department official said that even with the departure of non-essential personnel a large portion of U.S. personnel will remain in country; it is typical that such a departure would take a few days to complete.

The move came days after the administration said it was deploying an aircraft carrier strike group and bombers to the Middle East due to an unspecified threat posed by Iran and its proxies to American interests in the region.

But a senior British military officer directly contradicted the U.S. assessment on Tuesday, saying there was no heightened danger from Iran or its proxies in Iraq and Syria.

Maj. Gen. Christopher Ghika, deputy commander of Operation Inherent Resolve — the U.S.-led coalition fighting Islamic State in Iraq and Syria — said "there's been no increased threat from Iranian-backed forces in Iraq and Syria."

U.S. Central Command issued a statement disputing the British general's comments.

Democrats in Congress have accused the Trump administration of taking reckless actions and engaging in rhetoric that could trigger an unnecessary war with Iran.

The administration has defended its approach, saying it is merely seeking to safeguard U.S. personnel and making clear that it will respond if Iran or its proxies target Americans.