WASHINGTON (NYTIMES) - The Pentagon has abruptly sent the aircraft carrier Nimitz home from the Middle East and Africa over the objections of top military advisers.

This marks a reversal of a weeks-long muscle-flexing strategy aimed at deterring Iran from attacking United States troops and diplomats in the Persian Gulf.

Officials said on Friday (Jan 1) that the acting defence secretary, Mr Christopher Miller, had ordered the redeployment of the ship as a "de-escalatory" signal to Teheran to avoid stumbling into a crisis in President Donald Trump's waning days in office.

US intelligence reports indicate that Iran and its proxies may be preparing a strike as early as this weekend to avenge the death of Major General Qasem Soleimani, commander of Iran's elite Quds Force of the Revolutionary Guard.

Senior Pentagon officials said Mr Miller assessed that dispatching the Nimitz now, before the anniversary this Sunday of Maj Gen Soleimani's death in a US drone strike in Iraq, could remove what Iranian hardliners see as a provocation that justifies their threats against US military targets. Some analysts said the return of the Nimitz to its home port of Bremerton, Washington, was a welcome reduction in tensions between the two countries.

"If the Nimitz is departing, that could be because the Pentagon believes that the threat could subside somewhat," said Mr Michael P. Mulroy, the Pentagon's former top Middle East policy official.

Critics said the mixed messaging was another example of the inexperience and confusing decision-making at the Pentagon since Mr Trump fired defence secretary Mark Esper and several of his top aides in November, and replaced them with Mr Miller, a former White House counterterrorism aide, and several Trump loyalists.

"This decision sends at best a mixed signal to Iran, and reduces our range of options at precisely the wrong time," said Mr Matthew Spence, a former top Pentagon Middle East policy official. "It calls into serious question what the administration's strategy is here."

Mr Miller's order overruled a request from General Kenneth F. McKenzie Jr, commander of American forces in the Middle East, to extend the deployment of the Nimitz and keep its formidable wing of attack aircraft at the ready.

In recent weeks, Mr Trump has repeatedly threatened Iran on Twitter, and in November, top national security aides talked the President out of a pre-emptive strike against an Iranian nuclear site. It is unclear whether Mr Trump was aware of Mr Miller's order to send the Nimitz home.

The Pentagon and Gen McKenzie's Central Command had for weeks publicised several shows of force to warn Teheran of the consequences of any assault. The Nimitz and other warships arrived to provide air cover for American troops withdrawing from Iraq, Afghanistan and Somalia. The Air Force three times dispatched B-52 bombers to fly within some 100km of the Iranian coast. And the Navy announced for the first time in nearly a decade that it had ordered a Tomahawk-missile-firing submarine into the Persian Gulf.

As recently as Wednesday, Gen McKenzie warned the Iranians and their Shi'ite militia proxies in Iraq against any attacks around the anniversary of Maj Gen Soleimani's death on Sunday.

But on Thursday, senior military advisers, including Gen McKenzie and General Mark Milley, chairman of the Joint Chiefs of Staff, were surprised by Mr Miller's decision on the Nimitz.

The Navy had sought to limit more extensions to the carrier's already lengthy deployment, but commanders believed the warship would stay at least another several days to help counter what military intelligence analysts considered a growing and imminent threat.

US intelligence analysts in recent days said they have detected Iranian air defences, maritime forces and other security units on higher alert. They have also determined that Iran has moved more short-range missiles and drones into Iraq. But senior Defence Department officials acknowledge they cannot tell if Iran or its Shi'ite proxies in Iraq are readying to strike US troops or are preparing defensive measures in case Mr Trump orders a pre-emptive attack against them.

"What you have here is a classic security dilemma, where manoeuvres on both sides can be misread and increase risks of miscalculation," said Mr Brett McGurk, Mr Trump's former special envoy to the coalition to defeat the Islamic State in Iraq and Syria (ISIS) group.

Some top aides to Mr Miller, including Mr Ezra Cohen-Watnick, one of the White House loyalists newly installed as the Pentagon's top intelligence policy official, raised doubts about the deterrence value of the Nimitz, especially when balanced against the morale costs of extending its tour. Some aides also questioned the imminence of any attack by Iran or its proxies, an assessment reported earlier by CNN.

Pentagon officials said they had sent additional land-based fighter and attack jets, as well as refuelling planes, to Saudi Arabia and other gulf countries to offset the loss of the Nimitz's firepower.

On Friday, the top commander of Iran's paramilitary Revolutionary Guard said his country was fully prepared to respond to any US military pressure amid heightened tensions between Teheran and Washington in the waning days of Mr Trump's presidency.

"Today, we have no problem, concern or apprehension toward encountering any powers," Maj Gen Hossein Salami said at a ceremony at Teheran University commemorating the anniversary of Maj Gen Soleimani's death.

"We will give our final words to our enemies on the battlefield," Maj Gen Salami said, without mentioning the US directly.

Iran's foreign minister, Mr Javad Zarif, said on Thursday that the Trump administration was creating a pretext for war.

"Instead of fighting Covid in US, @realDonaldTrump & cohorts waste billions to fly B52s & send armadas to OUR region," Mr Zarif said in a tweet. "Intelligence from Iraq indicate plot to fabricate pretext for war. iran doesn't seek war but will openly & directly defend its people, security & vital interests."

In another provocation from Iran on Friday, Teheran notified international inspectors that it was about to begin producing uranium at a significantly higher level of enrichment at Fordo, a plant that is deep under a mountain and thus harder to attack. The move seemed primarily aimed at putting pressure on President-elect Joe Biden to rejoin the nuclear agreement with Iran. There was little activity permitted at the Fordo plant under the 2015 deal.

The notification to the International Atomic Energy Agency in Vienna, the United Nations group that oversees the production of nuclear material, said that Iran would resume production of uranium enriched to 20 per cent purity. That is the highest level it produced before the nuclear deal, which the country justified at the time as necessary to make medical isotopes for its Teheran Research Reactor.

Fuel enriched to that level is not sufficient to produce a bomb, but it is close. It requires relatively little further enrichment to get to the 90 per cent purity that is traditionally used for bomb-grade fuel.

The move was not unexpected. Iran's Parliament passed legislation recently requiring the government to increase both the quantity of fuel it is making and the enrichment level. But the choice of doing that production at Fordo, its newest facility, was telling. The plant is built deep underneath a mountain at a well-protected Revolutionary Guard base, and successfully striking it would require repeated attacks with the largest bunker-busting bomb in the American arsenal.

It would take months for Iran to produce any significant amount of fuel at the 20 per cent enrichment level, but the mere announcement could be another red flag for Mr Trump to rekindle bombing options.