Speaking to reporters on the day the Iranian military shot down a US drone in the Strait of Hormuz, the president said he believed Tehran may have erred and that he believed a “a general or somebody” mistakenly ordered the attack.

Asked he was planning to respond militarily, he said people would “find out”. Asked he was being pressured by others in his administration, the president, who was meeting in the Oval Office with Canadian prime minister Justin Trudeau, said this was not the case.

“No no not at all. In fact in many cases it’s the opposite. But I will say, look, I said I want to get out of these endless wars, I campaigned on that, I want to get out. We’ve been in Afghanistan for 19 years,” he said.

“We beat the caliphate. We took back the 100 per cent of the caliphate. At 99 per cent, Justin, I said we’re going to get out we’re going to start peeling back and everybody went crazy because it was 99, and so I said all right, so we’ll finish it up. So we got 100 per cent. And we’re pulling that back out of Syria. We’re pulling a lot of people back.”

The Islamic Republic of Iran 40 years on Show all 20 1 /20 The Islamic Republic of Iran 40 years on The Islamic Republic of Iran 40 years on Women praying during Ashura festivities in Yazd in February Jan Schneider The Islamic Republic of Iran 40 years on Cars cemented in at the Holy Defence Museum-Garden in Khorramshahr – in 1980 occupying Iraqi forces used such formations to deter paratrooper landings Jan Schneider The Islamic Republic of Iran 40 years on Women on the Si-o-se-pol bridge over the Zayanderude river in Esfahan Jan Schneider The Islamic Republic of Iran 40 years on Iranian tourists at Vank cathedral in the Armenian quarter in the city of Esfahan Jan Schneider The Islamic Republic of Iran 40 years on A reddened fountain in Yazd – a national motif recalling the countries ‘martyrs’ Pictures by Jan Schneider The Islamic Republic of Iran 40 years on Prayers before a list naming the fallen of the Iran-Iraq war in Tehran Jan Schneider The Islamic Republic of Iran 40 years on In a museum in central Tehran, a wax figure of Ayatollah Khomeini Jan Schneider The Islamic Republic of Iran 40 years on Carom billiards in Tehran Jan Schneider The Islamic Republic of Iran 40 years on Nearly two thirds of Iran’s population is under-30 Jan Schneider The Islamic Republic of Iran 40 years on Sanctions are exacerbating poverty Jan Schneider The Islamic Republic of Iran 40 years on Young people are adept at catching moments of freedom, such as this one in the capital Jan Schneider The Islamic Republic of Iran 40 years on At an art auction in Tehran, the wealthy turn out Jan Schneider The Islamic Republic of Iran 40 years on Propaganda murals are everywhere Jan Schneider The Islamic Republic of Iran 40 years on Tehranis love their outdoor spaces too Jan Schneider The Islamic Republic of Iran 40 years on The hypersaline waters of Lake Urmia are fast diminishing – Iran faces ecological catastrophe Jan Schneider The Islamic Republic of Iran 40 years on A martyr is depicted outside the huge Beheshte-e-Zahra cemetery in Tehran Jan Schneider The Islamic Republic of Iran 40 years on A guard naps outside Iran’s foremost tourist attraction – the ancient ruins of Persepolis Jan Schneider The Islamic Republic of Iran 40 years on Memorial to Iranian pilgrims who died during a stampede in Mecca 1987 Jan Schneider The Islamic Republic of Iran 40 years on The martyr fixation on display in the southern city of Shush Jan Schneider The Islamic Republic of Iran 40 years on Emamzadeh Saleh mosque in Shemiran, Tehran Jan Schneider

Mr Trump’s tone appeared in contrast to a number of members of his administration, among them secretary of state Mike Pompeo and national security advisor John Bolton, who have adopted a hardline stance towards Iran, since the president last year pulled the US out of the Iran Nuclear Deal. Both have accused Tehran of being behind attacks on tankers in the Gulf, something Iran has denied.

“This is a new wrinkle, a new fly in the ointment what happened, shooting down a drone,” said the president. “And this country will not stand for it, that I can tell you.”

Later on Thursday, Mr Trump met with congressional leaders to discuss the escalating feud with Iran, against which the US has imposed debilitating sanctions and reportedly launched an disinformation war.

Lindsey Graham: Iran needs to get ready for 'severe pain'

After the meeting, senior Democrats warned that Mr Trump would require authorisation from Congress before launching military action. House speaker Nancy Pelosi said the administration should engage with its allies “and do everything in our power to de-escalate”.

Meanwhile, several Republican leaders, among them Kevin McCarthy, said there must be a "measured response" to Iran's actions. “Iran directly attacked a United States asset over international waters. This provocation comes a week after they attacked and destroyed two commercial tankers in international waters,” he said in a statement.

Earlier this week, it emerged Iran was set to breach the level of uranium enrichment set in place by the multi-party 2015 deal Mr Trump withdrew Washington from, an announcement that was seen as an attempt by Tehran to try and pressure the European signatories to the deal to help it counter the impact of US sanctions.

“Obviously we are very concerned about the escalation by Iran recently because we have a significant presence in the area, including a Nato mission in Baghdad and Iraq,” Mr Trudeau said.

“We look forward to discussing...with our closest ally, how we move forward as an international community.”

The circumstances of the shooting down of the drone, a US navy RQ-4A Global Hawk, by Iran’s Revolutionary Guard, are disputed.

Iran said the drone, with a wingspan larger than a Boeing 737 and costing more than over $100m, had violated its territorial airspace.

The US called the missile fire “an unprovoked attack” in international airspace. Either way, it marked the first time Iran had struck the US military, which released a set of coordinates it claimed the drone was shot down at.

Iranian foreign minister Mohammad Javad Zarif said on Twitter the aircraft had taken off from the United Arab Emirates “in stealth mode & violated Iranian airspace”.

A Iranian Revolutionary Guards statement said the drone's identification transponder had been switched off “in violation of aviation rules and was moving in full secrecy” when it was downed, Iranian state broadcaster IRIB reported.