The acting US defence secretary has claimed that the alleged threat from Iran has receded as the result of an American show of force in the Middle East.

“We’ve put on hold the potential for attacks on Americans,” Patrick Shanahan told reporters before briefing Congress on the situation in the Persian Gulf and the military deployments that the US said were a response to a danger of imminent attack.

The arrival of an aircraft carrier and its accompanying ships was recently accelerated, and B-52 bombers were sent to Qatar. Tensions increased with mysterious sabotage attacks on oil tankers in the Gulf, and drone strikes on Saudi oil installations, claimed by Iranian-backed Houthi rebels in Yemen.

Nerves in the region were put even more on edge on Sunday by Donald Trump’s tweeted threat that any conflict with the US would mean “the official end of Iran”.

The remarks from Shanahan appeared to be a sign that tensions were easing.

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Asked what he meant by saying that the threat was “on hold”, the acting defence secretary said: “There haven’t been any attacks on Americans. I would consider that a hold.

“That doesn’t mean that the threats that we’ve previously identified have gone away,” Shanahan added. “Our prudent response, I think, has given the Iranians time to recalculate. I think our response was a measure of our will and our resolve that we will protect our people and our interests in the region.”

The Trump administration did not make public the intelligence it claimed showed an imminent Iranian threat to the US in the Middle East.

An investigation is under way into the sabotage attacks on four oil tankers off the coast of the United Arab Emirates last week. The UK and Norway are helping the US with the inquiry, which was expected to report on Monday, but has been delayed for reasons that have not made clear.

One of the tankers attacked was Norwegian-flagged. The secretary of state, spoke on Tuesday with the country’s foreign minister, Ine Søreide, about the incident.

A European diplomat said: “We are very careful not to make attribution for recent attacks unless we are certain.”

Officials briefing the media have also claimed that overhead photography showed missiles being loaded on to dhows on the Iranian coast, and chatter about potential attacks on US facilities and personnel in Iraq. The state department withdrew non-essential staff from its embassy in Baghdad and consulate in Erbil.

It was unclear what Iran’s aim was supposed to be in loading missiles on to dhows. Experts said that it would be very difficult to fire a missile from a small boat and if the intelligence reports were true, it was more likely they were being shipped to the Houthi movement in Yemen, or moved for safekeeping.

Later reports suggested that the Iranian military deployments and discussion of targets could have been contingency measures for a possible response in the event of a US attack on Iran, seen as increasingly likely in recent months with the apparent ascendancy of John Bolton, the ultra-hawk national security adviser, in foreign policymaking.

The secretary of state, Mike Pompeo and the chairman of the joint chiefs of staff, General Joseph Dunford, were expected to brief the House and Senate on Iran on Tuesday afternoon. Bolton was not on the list of speakers.

“My take is that the Iranians saw an attack coming and they prepared to strike back and that caused alarm in the White House and particularly with the president,” said Trita Parsi, founder of the National Iranian American Council, who now teaches at Georgetown University.

“The line sold to Trump by Bolton and Bibi Netanyahu and Mohammed bin Salman is he could strike Iran, show US dominance, and not risk anything. Iran showed it was preparing to strike back. Trump is smart enough to know that a war would be devastating, and not just for his political interests.”

Behnam Ben Taleblu, a senior fellow at the Foundation for Defense of Democracies, argued that the current defusing of tensions showed that the US response had worked.

“The entire point behind America’s military repositioning in the region was to dampen the prospects of escalation,” Taleblu said. “And while it may have worked for now, Washington will need to make sure its message of resolve is similarly interpreted in the future. The Iranians have a habit of continually testing for weaknesses and deficiencies.”