WASHINGTON — The U.S. military's decision to surge a carrier strike group and Air Force bombers to the Middle East was based on Iranian threats to U.S. military forces and civilians at multiple locations in the region, according to U.S. officials and a defense official.

Recent intelligence showed Iran and its proxies are repositioning forces and may be planning for attacks, both at land and at sea, the officials said.

The troubling new intelligence caused the commander of the U.S. Central Command, Gen. Frank McKenzie, to request more assets to his area of responsibility. Acting Secretary of Defense Patrick Shanahan approved the request to redirect the USS Abraham Lincoln Carrier Strike Group to the Persian Gulf and to move a bomber task force to the region.

Shanahan tweeted Monday that he approved the deployment Sunday afternoon, calling it "a prudent repositioning of assets in response to indications of a credible threat by Iranian regime forces." Shanahan called on the Iranians to "cease all provocation," warning that the United States "will hold the Iranian regime accountable for any attack on U.S. forces or our interests."

The officials warned Iran has proxy forces operating in Iraq, Syria, Yemen and other parts of the region who could rise up and target Americans. "We are taking this threat reporting very seriously," one U.S. official said.

The unusual announcement telegraphing the location of a carrier strike group deployment came late Sunday night in a statement from national security adviser John Bolton.

"In response to a number of troubling and escalatory indications and warnings, the United States is deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the U.S. Central Command region 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," the statement said. "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."

On Monday, acting Pentagon spokesperson Charles E. Summers Jr. said, "The deployment of the USS Abraham Lincoln Carrier Strike Group and a bomber task force are considered a prudent step in response to indications of heightened Iranian readiness to conduct offensive operations against U.S. forces and our interests."

1 of 2: Last night's announced deployment of the @CVN_72 and a @USAirForce bomber task force to the @CENTCOM area of responsibility, which I approved yesterday, represents a prudent repositioning of assets in response to indications of a credible threat by Iranian regime forces. — Acting SecDef Pat Shanahan (@ActingSecDef) May 6, 2019

Brett McGurk, the former U.S. envoy for the fight against ISIS and now an NBC News analyst, said on MSNBC on Monday that it would have been better to convey such a strong message privately, and he didn't think it was "smart" to cut off all diplomatic channels and all communication with the Iranians.

"In the middle of the Cold War, Ronald Reagan railed against the Soviet Union as an evil empire and we still had multiple channels of diplomacy open. I think that's smart. Right now, we have no channels of diplomacy open. So the risk of a clash, the risk of an inadvertent conflict, is increasing."

"This is a president who is clearly willing to put the military option back on the table in a credible way, and [the carrier group and bombers] reinforce the administration’s willingness to use military power if circumstances warrant it," said Mark Dubowitz of the Foundation for Defense of Democracies, which has favored imposing tough sanctions on Iran.

But Dylan Williams, vice president of the J Street advocacy group, which has sharply criticized the administration’s approach to Iran, said the White House appeared to be laying the ground for war.

“With aggressive statements about the deployment of U.S. warships to the region and other belligerent rhetoric," Williams said, "the Trump administration is laying the groundwork for an unnecessary new war of choice which Congress has not authorized and which the American people do not want. It’s now vital that lawmakers take responsible steps to head off this steady march towards armed conflict — before it’s too late."

Iran may scale back compliance with nuke deal

As the U.S. flexed its military muscle in the Middle East, Iran on Monday signaled it may scale back its compliance with the 2015 nuclear agreement, the JCPOA, after the Trump administration tightened economic sanctions on the regime.

President Donald Trump pulled the U.S. out of the deal between Iran and world powers a year ago, but Tehran has so far abided by the agreement, which placed limits on its nuclear program in return for a relaxation of U.S. and international sanctions. Since withdrawing from the deal, the Trump administration has reimposed hard-hitting economic sanctions, including measures designed to choke off Iran's crucial oil exports.

Iran will not withdraw from the deal but will reduce its commitments and resume some nuclear activities, according to the state-run Iranian Students' News Agency. Iranian President Hassan Rouhani planned to announce the changes Wednesday, ISNA said.

Iranian state media suggested Iran possibly would no longer adhere to limits on uranium enrichment imposed by the nuclear agreement. Highly enriched uranium can be used as material for an atomic bomb.

Last Friday, the administration announced it was scrapping waivers that allowed Iran to ship out heavy water and excess enriched uranium to Oman and Russia. The move could make it difficult for Iran to dispose of enriched uranium and stay within the limits of the 2015 deal.

Iranian and European officials are due to meet in Brussels on Tuesday to discuss the next steps after the latest round of sanctions unveiled by the Trump administration.