WASHINGTON — Senior American officials said on Monday that new threats by Iran against United States troops in Iraq were behind the sudden deployment of an aircraft carrier strike group and Air Force bombers to the Persian Gulf.
The White House and Pentagon made the decision after seeing intelligence that showed new activity on the part of Iranian-aligned forces since Friday, said two senior officials who spoke on condition of anonymity.
Additionally, one official noted new concerns in waterways where Iranian maritime forces operate.
The officials would not provide specific details about the threat posed by Iranian forces or Iraqi Shiite militias with ties to Tehran’s military. Col. Scott Rawlinson, a spokesman for the American-led military coalition in Iraq, declined to comment.
The new movement of American military forces was announced by John R. Bolton, the national security adviser, on Sunday night.
The deployment of the aircraft carrier U.S.S. Abraham Lincoln was intended “to send a clear and unmistakable message to the Iranian regime that any attack on United States interests or on those of our allies will be met with unrelenting force,” Mr. Bolton said in a statement.
He added that “the United States is not seeking war with the Iranian regime, but we are fully prepared to respond to any attack, whether by proxy, the Islamic Revolutionary Guards Corps or regular Iranian forces.”
Earlier this year, President Trump notably backed up assertions by Mr. Bolton that the 5,200 American troops currently in Iraq should stay there to “watch Iran.” Iraqi leaders quickly pushed back, saying they feared that the United States was trying to use its troop presence in Iraq to further its own goals of isolating Iran.
Mr. Trump at the time harkened back to his brief visit in December to see American troops at Al-Asad base in western Iraq and suggested that United States forces there could be used to carry out surveillance on Iran.
The new assertion that Iran or its proxies are planning attacks on American troops in Iraq is bound to spark more questions from Iraqi political leaders about whether the Trump administration is trying to use its military presence to further its agenda against Tehran.
The two senior American officials said new intelligence raised concerns about the Revolutionary Guards and their activities in Iraq. The group is an arm of the Iranian military that has helped train Shiite Arab militias in Iraq.
An elite unit of the Iranian guards, the Quds Force, has been particularly active in helping the militias and the Shiite-led Iraqi government fight the Islamic State, a Sunni extremist group that the American military is also fighting.
Senator Marco Rubio, a Republican of Florida and member of the Senate Foreign Relations Committee, gave a stern warning Monday morning about the militias and the Revolutionary Guards.
“We will not distinguish between attacks from Shia militias in #Iraq and the #IRGC that controls them,” he wrote on Twitter. “Any attack by these groups against U.S. forces will be considered an attack by #Iran & responded to accordingly.”
Secretary of State Mike Pompeo told reporters on Sunday night during a flight to Finland of signs of growing threat from the Iranians.
“It is absolutely the case that we’ve seen escalatory action from the Iranians, and it is equally the case that we will hold the Iranians accountable for attacks on American interests,” he said. “The fact that those actions take place, if they do, by some third-party proxy, whether that’s a Shia militia group or the Houthis or Hezbollah, we will hold the Iranians — Iranian leadership — directly accountable for that.”
Last month, the Trump administration designated the Revolutionary Guards as a terrorist organization. The move imposes economic penalties and travel restrictions on members of the group, a unit of Iran’s military, and anyone else who deals with it. The terrorist designation was the first time the United States had made that move against a part of another nation’s government.
Although Mr. Bolton and Mr. Pompeo pushed hard for the designation, defense and intelligence officials opposed it out of concern Iran would take reciprocal action against American military personnel and intelligence operatives or launch attacks.
On Tuesday, President Hassan Rouhani of Iran signed a bill into law that declared all American troops in the Middle East terrorists and labeled the United States government a state sponsor of terrorism.
American officials have recently debated whether to designate some of the Shiite militias in Iraq as foreign terrorist organizations, even though Iraqi officials who are partners with the Americans opposed any such move. Iranian forces and their proxy fighters have generally refrained from attacking American troops in recent years.
The Iraqi militias — some of which were trained by the Revolutionary Guards — operate with Baghdad’s approval and financing. Several are legitimate players in Iraqi politics. Representatives of the militias did well in general elections last year and hold parliamentary seats. They are part of the Popular Mobilization Forces, an umbrella organization of about 50 paramilitary groups that have fought the Islamic State.
At the height of the Iraq war in the mid-2000s, Iranian military officials helped train Iraqi Shiite militias to fight American troops and aided in the building of powerful explosive devices used against American armored vehicles. The Pentagon has said at least 603 American personnel were killed in Iraq by Iran-backed fighters — 17 percent of all Americans killed in hostile action there.
Last month, Republican and Democratic senators asked Mr. Pompeo whether the administration would explicitly seek congressional approval before trying to enter a war with Iran. Mr. Pompeo demurred, saying lawyers should answer that question.
Senator Rand Paul, Republican of Kentucky, insisted that the United States could not attack Iran as part of a war authorization allowing the use of military force against Al Qaeda and other extremist groups deemed responsible for the attacks of Sept. 11, 2001.
Mr. Pompeo has said Iran bears more responsibility for ongoing violence in the Middle East than any other actor, even though the American military has been focused on fighting the Islamic State.
The Trump administration has taken a hard-line policy against Iran and has said it aims to force Iran to lessen or end its support for Shiite militias and other groups across the Middle East.
One year ago, Mr. Trump withdrew from a nuclear deal that world powers had reached with Iran in 2015, and he has since imposed harsh sanctions intended to force political change in Tehran. Mr. Bolton and Mr. Pompeo have been the leaders in formulating the new hard-line policies, often in direct opposition to recommendations from the Defense Department and C.I.A.