Officials said the options include increasing the number of troops in the region from between 60,000 and 80,000 to more than 100,000 in the most dramatic scenario were Iran to attack US interests or make clear moves to develop a nuclear weapon. The New York Times on Monday reported that acting Defence Secretary Patrick Shanahan, in response to a request for updated options from national security adviser John Bolton, put forward several proposals, including one to deploy 120,000 troops. US President Donald Trump has warned Tehran not to strike US forces in the Middle East. Credit:Bloomberg Speaking to reporters in Washington, Trump characterised the article as inaccurate but said he would be prepared to authorise an even more muscular approach if needed. "Hopefully we're not going to have to plan for that," he said. "And if we did that, we'd send a hell of a lot more troops than that."

Trump's views on the proposals were not immediately clear. In general, he has sided with ending US military involvement in wars overseas, although he has identified Iran as a chief adversary and sought to demonstrate a tough stance on nations challenging the United States. He is surrounded by officials with hard-line views on Iran led by his National Security Advisor John Bolton, who has advocated for regime change in Iran. Iranian worshippers burn a US flag during a rally after Friday prayer in Tehran. Credit:AP Iranian and American leaders say they do not want a war but warn that they are prepared to use military might if provoked. Speaking during a visit to Sochi, Russia, on Tuesday, US Secretary of State Mike Pompeo said he had made clear "that if American interests are attacked, we will most certainly respond in an appropriate fashion." Ayatollah Khamenei, in a series of messages on Twitter, also warned the US would be forced to withdraw from a confrontation with Iran.

"We don't seek a war nor do they," he said. "They know a war wouldn't be beneficial for them." Nevertheless, the increasing tension has fuelled concern that the two countries might accidentally slide into conflict, with Britain and the European Union encouraging further negotiation on the deal. Ayatollah Ali Khamenei speaks in a meeting with governmental officials in Tehran on Tuesday. Credit:AP Trump withdrew from the 2015 deal last year. It was signed with Iran, the US, UK, France, China, Russia and Germany to ensure Iran would not enrich uranium in return for economic benefits and the gradual easing of sanctions. The comments from Khamenei and Pompeo came after four ships belonging to US allies Saudi Arabia, the United Arab Emirates and Norway were attacked near the Persian Gulf, an act for which US officials suggested Iran may be responsible.

The incident followed a series of US steps designed to isolate Iran, including the designation of its Islamic Revolutionary Guard Corps as a terrorist organisation and a raft of new sanctions. The damaged Emirati-flagged bunkering tanker A Michel off the coast of Fujairah, UAE. Credit:AP Becca Wasser, a policy analyst at Rand Corp, said those steps fuelled suspicions between the United States and its allies on one hand and Iran on the other, raising the risk of a small incident snowballing into a larger confrontation. "It's fairly common to have Iranian patrol boats harass US carriers and other ships in the strait," she said, referring to the Strait of Hormuz, a waterway off Iran that is key to global commerce. "You can imagine with some of the heightened tensions, that there could be a greater risk of that exploding into something larger."

"In different times, an accident or a mistake could be resolved because of open lines of communication between Iran and the United States," she added. "Now it could lead to the United States and Iran accidentally stumbling into some form of escalation." Typically a range of options is presented by military officials when requested by civilian leaders. Sometimes, policymakers select one course of action. Other times, they decide to do nothing. The Saudi-flagged oil tanker Amjad anchored off the coast of Fujairah was one of four "sabotaged" ships. Credit:Maxar/AP US Central Command maintains a host of contingency plans that are updated periodically, especially when policy or threat information changes. Military officials, who have privately voiced a strong desire to avoid conflict with Iran, have nevertheless described the recent intelligence as sobering and say they believe that Iran is actively planning attacks on US forces.

Captain Bill Urban, a spokesman for US Central Command, said the alert level for forces in Iraq and Syria had been increased in response to the recent intelligence, pushing back against a statement by a British general serving in Baghdad as part of the US-led coalition who said there was no amplified threat from Iranian backed forces there. That operation "is now at a high level of alert as we continue to closely monitor credible and possibly imminent threats to US forces in Iraq," Urban said. More than 5000 US troops are in Iraq, and less than half that are in neighbouring Syria. Pentagon and congressional officials said the elements that contributed to the worrisome intelligence picture included Iranian military and other threats against diplomatic facilities in Baghdad and Erbil, Iraq. Officials also said they believed that Iran may be preparing to mount rocket or missile launchers on small ships. Military officials say they do not know why Iran appears to be embracing a more hostile stance but say it is probably a result of mounting economic and diplomatic pressures. Since the United States withdrew from the nuclear agreement a year ago, it has penalised almost 1000 Iranian individuals and entities. Sanctions on financial transactions and oil exports, in particular, have had a devastating effect on the Iranian economy.

International nuclear monitors have said that Iran has continued to meet its commitments under the 2015 agreement but that it has threatened to resume the stockpiling of enriched uranium unless the European Union finds a way to facilitate sanctions relief within 60 days. The Europeans, while striving to keep the nuclear accord alive, are stuck between the hard-line positions staked out by Washington and Tehran. The uptick in tensions has also rattled the State Department's top officials in charge of diplomatic security, who on Tuesday postponed a major forum of regional security officers from most embassies and consulates worldwideas senior personnel need to "remain in the field to assess and respond to potential threats," according to a State Department memo. The damaged Norwegian-flagged oil tanker MT Andrea Victory off the coast of Fujairah, UAE, on Monday. Credit:UAE/AP The event is scheduled every three to four years and involves 300-plus people, said a State Department official, who spoke on the condition of anonymity because he was not authorised to discuss internal logistics. "It's no small potatoes that Diplomatic Security chose to cancel this," the official said. Making matters more complicated, Yemen's Houthi rebels, who are often accused of being Iranian proxies, carried out multiple drone attacks on Saudi oil facilities on Tuesday, a day after the Saudi Arabia oil tankers were damaged.