WASHINGTON (NYTIMES) - At a meeting of President Donald Trump's top national security aides last Thursday (May 9), Acting Defence Secretary Patrick Shanahan presented an updated military plan that envisions sending as many as 120,000 troops to the Middle East should Iran attack US forces or accelerate work on nuclear weapons, administration officials said.

The revisions were ordered by hardliners led by Mr John Bolton, Mr Trump's national security adviser. It does not call for a land invasion of Iran, which would require vastly more troops, officials said.

The development reflects the influence of Mr Bolton, one of the administration's most virulent Iran hawks, whose push for confrontation with Teheran was ignored more than a decade ago by president George W. Bush.

It is highly uncertain whether Mr Trump, who has sought to disentangle the United States from Afghanistan and Syria, ultimately would send so many US forces back to the Middle East.

It is also unclear whether the President has been briefed on the number of troops or other details in the plans. On Monday (May 13), when asked about if he was seeking regime change in Iran, Mr Trump said: "We'll see what happens with Iran. If they do anything, it would be a very bad mistake."

There are sharp divisions in the administration over how to respond to Iran at a time when tensions are rising about Iran's nuclear policy and its intentions in the Middle East.

Some senior US officials said the plans, even at a very preliminary stage, show how dangerous the threat from Iran has become. Others, who are urging a diplomatic resolution to the current tensions, said it amounts to a scare tactic to warn Iran against new aggressions.

European allies who met Secretary of State Mike Pompeo on Monday said that they worry that tensions between Washington and Teheran could boil over, possibly inadvertently.

More than a half-dozen US national security officials who have been briefed on details of the updated plans agreed to discuss them with The New York Times on the condition of anonymity. Spokesmen for Mr Shanahan and General Joseph F. Dunford Jr, the chairman of the Joint Chiefs of Staff, declined to comment.

The size of the force involved has shocked some who have been briefed on them. The 120,000 troops would approach the size of the US force that invaded Iraq in 2003.

Deploying such a robust air, land and naval force would give Teheran more targets to strike, and potentially more reason to do so, risking entangling the US in a drawn out conflict. It also would reverse years of retrenching by the US military in the Middle East that began with president Barack Obama's withdrawal of troops from Iraq in 2011.

But two of the US national security officials said Mr Trump's announced drawdown in December of American forces in Syria, and the diminished naval presence in the region, appear to have emboldened some leaders in Teheran and convinced the Islamic Revolutionary Guards Corps that the US has no appetite for a fight with Iran.

Several oil tankers were attacked or sabotaged off the coast of the United Arab Emirates over the weekend, raising fears that shipping lanes in the Persian Gulf could become flashpoints. "It's going to be a bad problem for Iran if something happens," Mr Trump said on Monday, when asked about the episode.

Emirati officials are investigating the apparent sabotage, and US officials suspect that Iran was involved. Several officials cautioned, however, that there is not yet any definitive evidence linking Iran or its proxies to the attacks. An Iranian Foreign Ministry spokesman called it a "regretful incident", according to a state news agency.

In Brussels, Mr Pompeo met the foreign ministers of Britain, France and Germany, co-signatories of the 2015 Iran nuclear deal, as well as with the European Union's foreign policy chief, Ms Federica Mogherini. He did not speak to the media, but the European officials said they had urged restraint upon Washington, fearing accidental escalation that could lead to conflict with Iran.

"We are very worried about the risk of a conflict happening by accident, with an escalation that is unintended really on either side," said British foreign secretary Jeremy Hunt.

The Iranian government has not threatened violence recently, but last week, President Hassan Rouhani said Iran would walk away from parts of the 2015 nuclear deal it reached with world powers. Mr Trump withdrew the US from the agreement a year ago, but European nations have urged Iran to stick with the deal and ignore Mr Trump's provocations.

The high-level review of the Pentagon's plans was presented during a meeting about broader Iran policy. It was held days after what the Trump administration described, without evidence, as new intelligence indicating that Iran was mobilising proxy groups in Iraq and Syria to attack US forces.

As a precaution, the Pentagon has moved an aircraft carrier, B-52 bombers, a Patriot missile interceptor battery and more naval firepower to the Gulf region.

At last week's meeting, Mr Shanahan gave an overview of the Pentagon's planning, then turned to Gen Dunford to detail various force options, officials said. The uppermost option called for deploying 120,000 troops, which would take weeks or months to complete.

Among those who attended last Thursday's meeting were Mr Shanahan, Mr Bolton, Gen Dunford, CIA director Gina Haspel, and director of national intelligence Dan Coats.

"The President has been clear, the United States does not seek war with Iran, and he is open to talks with Iranian leadership," Mr Garrett Marquis, a National Security Council spokesman, said on Monday in an e-mail. "However, Iran's default option for 40 years has been violence, and we are ready to defend US personnel and interests in the region."

The reduction of forces in the Middle East in recent years has been propelled by a new focus on China, Russia and a so-called Great Powers competition. The most recent National Defence Strategy - released before Mr Bolton joined the Trump administration - concluded that while the Middle East remains important, and Iran is a threat to American allies, the US must do more to ensure a rising China does not upend the world order.

As recently as late April, a US intelligence analysis indicated that Iran had no short-term desire to provoke a conflict. But new intelligence reports, including intercepts, imagery and other information, have since indicated that Iran was building up its proxy forces' readiness to fight and was preparing them to attack US forces in the region.

The new intelligence reports surfaced on the afternoon of May 3, Mr Shanahan told Congress last week. On May 5, Mr Bolton announced the first of new deployments to the Persian Gulf, including bombers and an aircraft carrier.

It is not clear to US intelligence officials what changed Iran's posture. But intelligence and Defence Department officials said American sanctions have been working better than originally expected, proving far more crippling to the Iranian economy - especially after a clampdown on all oil exports that was announced last month.

Also in April, the State Department designated the Revolutionary Guards a foreign terrorist organisation over objections from Pentagon and intelligence officials who feared reprisals from the Iranian military.

While much of the new intelligence appears to have focused on Iran readying its proxy forces, officials said they believed the most likely cause of a conflict will follow a provocative act, or outright attack, by the Revolutionary Guards' navy. The Guards' fleet of small boats has a history of approaching US Navy ships at high speed and Revolutionary Guards commanders have precarious control over their ill-disciplined naval forces.

Part of the updated planning appears to focus on what military action the US might take if Iran resumes its nuclear fuel production, which has been frozen under the 2015 agreement. It would be difficult for the Trump administration to make a case that the US was under imminent nuclear peril; Iran shipped 97 per cent of its fuel out of the country in 2016, and currently does not have enough to make a bomb.

That could change if Iran resumes enriching uranium. But it would take a year or more to build up a significant quantity of material, and longer to fashion it into a weapon. That would allow, at least in theory, plenty of time for the US to develop a response - like a further cut-off of oil revenues, covert action or military strikes.

The previous version of the Pentagon's war plan included a classified subset code-named Nitro Zeus, a cyber operation that called for unplugging Iran's major cities, its power grid and its military.

The idea was to use cyber weapons to paralyse Iran in the opening hours of any conflict, in hopes that it would obviate the need to drop any bombs or conduct a traditional attack. That plan required extensive presence inside Iran's networks - called "implants" or "beacons" - that would pave the way for injecting destabilising malware into Iranian systems.

Two officials said those plans have been constantly updated in recent years.

But even a cyber attack, without dropping bombs, carries significant risk. Iran has built up a major corps of its own, one that successfully attacked financial markets in 2012, a casino in Las Vegas and a range of military targets. US intelligence officials told Congress in January that Iranian hackers are now considered sophisticated operators who are increasingly capable of striking US targets.