Exactly what prompted the action was unclear, but it marked a further step in sharply rising tensions between the Trump administration and the Islamic Republic.
National security adviser John Bolton said Sunday night the U.S. was deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the Middle East, intending to send a message that "unrelenting force" will meet any attack on American forces or allies.
"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 Guard Corps or regular Iranian forces," Bolton said.
Neither Bolton nor other officials would provide any details about the supposed threat, which comes as the Trump administration wages a campaign of intensifying pressure against Iran and nearly a year after it withdrew from an Obama-era nuclear deal with Tehran.
In Iran, the semi-official ISNA news agency on Monday quoted an anonymous official as saying that Iranian President Hassan Rouhani planned a broadcast address Wednesday and might discuss "counteractions" Tehran will take over America's withdrawal from the international nuclear deal.
The agreement limited Iran's enrichment of uranium amid Western concerns that Tehran's program could allow it to build nuclear weapons. Iran insists its program is for peaceful purposes.
With its pressure campaign, the U.S. administration is trying to get Iran to halt activities such as supporting militant activities that destabilize the Middle East and threaten U.S. allies, including Israel, Secretary of State Mike Pompeo said.
"Our objective is to get the Islamic Republic of Iran to behave like a normal nation," Pompeo told reporters during a visit to Finland. "When they do that, we will welcome them back."
The order to the carrier group would get the Abraham Lincoln into the Middle East about two weeks earlier than initially planned following exercises in the Mediterranean region, according to a U.S. defense official who wasn't authorized to speak publicly, so spoke on the condition of anonymity. It forces the ships to cancel a planned stop in Croatia.
For years, the U.S. maintained a carrier presence in the Persian Gulf and Middle East region. During the height of the wars in Iraq and Afghanistan, there were two carriers in the area, but that was reduced to one.
Last year the administration decided to end the continuous carrier presence, and send a strike group only intermittently into the region. The U.S. Navy currently has no aircraft carrier in the Persian Gulf.
Bolton said the U.S. wants to send a message that "unrelenting force" will meet any attack on U.S. interests or those of America's allies.
Jon Alterman, senior vice president at the Center for Strategic & International Studies, questioned whether the U.S. adequately understands Iranian motivations and actions, and whether the military move was warranted.
"I don't think we should let the Iranians pull our chain at the time and place of their choosing," he said. "You can communicate seriousness to the Iranians without moving a lot of assets around, because moving assets is expensive and keeps assets from being in other places."
He added, however, that Iran has the capability to harm Americans, but it's difficult to assess the situation without knowing more about the intelligence that prompted the move.
Mark Dubowitz, who studies Iran for the Washington-based policy institute Foundation for Defense of Democracies, said a credible threat of overwhelming force "will make war less likely."
"If past is prologue, the regime will always move aggressively forward when it senses American weakness and recoil when it sensed American strength," Dubowitz said.
Along with the Lincoln, Bolton mentioned "a bomber task force," which suggested the Pentagon is deploying land-based bomber aircraft somewhere in the region, perhaps on the Arabian Peninsula.
Pompeo said the actions undertaken by the U.S. have been in the works for a while. The request for the accelerated move came over the weekend from the military's U.S. Central Command after reviewing various intelligence reports for some time, according to the U.S. official. Acting Defense Secretary Patrick Shanahan approved the request on Sunday.
"It is absolutely the case that we have seen escalatory actions from the Iranians and it is equally the case that we will hold the Iranians accountable for attacks on American interests," Pompeo said. "If these actions take place, if they do by some third-party proxy, a militia group, Hezbollah, we will hold the Iranian leadership directly accountable for that."
Asked about "escalatory actions," Pompeo replied, "I don't want to talk about what underlays it, but make no mistake, we have good reason to want to communicate clearly about how the Iranians should understand how we will respond to actions they may take."
Sen. Richard Blumenthal, D-Conn., a member of the Senate Armed Services Committee, said Monday that the carrier move sends an important message to Iran but the administration needs to give Congress more information.
"I worry that it could be misinterpreted," Blumenthal said. "I'm trusting that it isn't meant as a provocative act, but I need to know what the thought process and justifications are."
Asked if the Iranian action was related to the deadly events in Gaza and Israel — militants fired rockets into Israel on Sunday and Israel responded with airstrikes — Pompeo said, "It is separate from that."
The Trump administration has been intensifying its pressure campaign against Iran.
Last month, President Donald Trump announced the U.S. would no longer exempt any countries from U.S. sanctions if they continue to buy Iranian oil, a decision that primarily affects the five remaining major importers: China and India and U.S. treaty allies Japan, South Korea and Turkey.
The U.S. also recently designated Iran's Revolutionary Guard as a terrorist group, the first ever for an entire division of another government.
Trump withdrew from the Obama administration's landmark nuclear deal with Iran in May 2018 and, in the months that followed, reimposed punishing sanctions including those targeting Iran's oil, shipping and banking sectors.
Associated Press writers Robert Burns and Matthew Lee contributed to this report.