Move comes as Pentagon releases new photos in reported tanker attacks and Tehran sets 10-day deadline on nuclear deal.

Acting US Secretary of Defense Patrick Shanahan has announced the deployment of about 1,000 more troops to the Middle East for what he said were “defensive purposes”, citing concerns about a threat from Iran.

The announcement on Monday came amid fears of a confrontation between the United States and Iran in the wake of suspected attacks last Thursday on two tankers near the Strait of Hormuz, a vital shipping lane for the world’s oil supplies.

Washington and Tehran have traded accusations over the incidents.

“I have authorised approximately 1,000 additional troops for defensive purposes to address air, naval, and ground-based threats in the Middle East,” Shanahan said in a statement.

“The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behaviour by Iranian forces and their proxy groups that threaten United States personnel and interests across the region,” he said.

The new US deployment to the Middle East is in addition to a 1,500-troop increase announced last month, which came in response to attacks on four other tankers on May 12. Washington also sent warships and a Patriot missile defence battery to the region, citing unspecified threats from Iran.

Also on Monday, the Pentagon released new photos it claimed showed Iran was behind the suspected tanker attacks, while Tehran set a 10-day deadline for world powers to fulfil their commitments under a multilateral nuclear deal, saying it will otherwise surpass its uranium stockpile limit mandated by the accord.

Washington abandoned the deal last year and reinstated punishing economic sanctions on Iran.

“The United States does not seek conflict with Iran,” Shanahan said in his statement, adding the new deployment aimed “to ensure the safety and welfare of our military personnel working throughout the region and to protect our national interests”.

‘Small measure’

David Desroches, former director of NATO operations at the Pentagon, called the US troop move a “small measure”. He told Al Jazeera: “It’s designed to send a message, but this is nowhere near what you’d need for an invasion or a war.”

Meanwhile, the Pentagon has also released additional imagery of one of the ships damaged in Thursday’s incidents that it claimed supported its accusation Iran had carried out the suspected attacks.

The US accusation centres on an alleged unexploded limpet mine on the Kokuka Courageous tanker that the US said was removed by Iranian soldiers on a patrol boat.

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“Iran is responsible for the attack based on video evidence and the resources and proficiency needed to quickly remove the unexploded limpet mine,” the Pentagon said in a statement accompanying the new imagery.

Last week, the US released a grainy black and white video it said showed Iran’s Revolutionary Guard Corps (IRGC) removing a mine, but has not provided an explanation for why the alleged removal occurred while the US military was in the area.

The images released on Monday show the site where the unexploded mine was allegedly attached, the Iranians on a patrol boat who are said to have removed it, and damage from another device that did explode.

A US military image it says was taken from a US Navy helicopter in the Gulf of Oman, shows personnel the Pentagon says are members of the IRGC removing an alleged unexploded limpet mine from the Kokuka Courageous [US Navy/Handout via Reuters]

Iran’s armed forces chief of staff, Major General Mohammad Baqeri, denied on Monday that Tehran was behind the attacks and said if the Islamic Republic decided to block the Strait of Hormuz, it would do so publicly.

The secretary of Iran’s Supreme National Security Council, Ali Shamkhani, said Tehran was responsible for security in the Gulf and urged US forces to leave the region, state TV said.

The latest developments drew concern from China, with State Councillor Wang Yi calling on all sides to ease tensions on Tuesday.

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“We call on all sides to remain rational and exercise restraint, and not take any escalatory actions that irritate regional tensions, and not open a Pandora’s box,” Wang said.

“In particular, the US side should alter its extreme pressure methods. Any unilateral behaviour has no basis in international law,” Wang said, warning that it could create “an even greater crisis”. The Iran nuclear deal was the only feasible way to resolve its nuclear issue, he said, urging Iran to be “cautious with its decision-making and not lightly abandon this agreement”.

‘Crucial moment’

The 2015 accord, which Iran and the other signatories – the United Kingdom, France, Germany, China and Russia – have maintained following Washington’s decision, caps Iran’s stock of low-enriched uranium at 300 kg enriched to 3.67 percent, well below weapons-grade levels of around 90 percent.

Behrouz Kamalvandi, spokesman for Iran’s Atomic Energy Organization spokesman said: “We have quadrupled the rate of enrichment [of uranium] and even increased it more recently, so that in 10 days it will bypass the 300 kg limit.”

“Iran’s reserves are every day increasing at a more rapid rate,” he told state TV, adding that “the move will be reversed once other parties fulfil their commitments.”

Morgan Ortagus, spokeswoman for US Department of State, said the world “should not yield to nuclear extortion.” She added: “It’s unfortunate that they’ve made this announcement today but I said earlier it doesn’t surprise anybody”.

For his part, Iran’s President Hassan Rouhani said on Monday that European nations still had time to save the accord.

“It’s a crucial moment, and France can still work with other signatories of the deal and play a historic role to save the deal in this very short time,” Rouhani was quoted as saying during a meeting with France’s new ambassador in Iran.

Germany, France and Britain have rejected the ultimatum, with French President Emmanuel Macron saying he regretted Tehran’s latest announcements and urging it “to behave in a way that is patient and responsible.”

Max Blumenthal, editor of GrayzoneProject.com, said the message from the US is that they intend on continuing to escalate the crisis, triggered by Washington’s decision last year to exit an international accord.

“The US is stepping up its maximum pressure strategy in a show of force that’s part of a two-year long undeclared war on Iran that includes what Iranian Foreign Minister Mohammad Javad Zarif has correctly called ‘financial terrorism’,” he told Al Jazeera.

“At this point, Iran feels cornered and it’s taking its own measures to respond. And I think we are in an extremely dangerous situation and conflict could break out – something that extreme elements of Trump admin might actually be excited for.

“It’s no way to deny that Trump administration has embarked on a strategy of regime change which Iran will never accept.”