US considers response to shooting down of US drone that Tehran claims was flying in Iranian airspace

US security officials have been summoned to the White House to discuss a response to the shooting down of a US spy drone, which Donald Trump has called a “big mistake” by Tehran.

Iran said it shot down the unmanned aircraft in its airspace. The US military has said it was downed over international waters in the strait of Hormuz.

A meeting of senior security officials, including the chairman of the joint chiefs of staff, Gen Joseph Dunford, convened in the White House on Thursday morning to discuss how to react. As his officials were conferring, Trump tweeted: “Iran made a very big mistake!”

But the US president later appeared to play down the incident, saying that the drone could have been shot down “by mistake.”

“I think probably Iran made a mistake - I would imagine it was a general or somebody that made a mistake in shooting that drone down,” he told reporters during an appearance with Canadian Prime Minister Justin Trudeau. He was coy about whether the U.S. would respond, saying only that “you’ll find out.”

Earlier the president chaired a meeting with his national security adviser, John Bolton; the secretary of state, Mike Pompeo and the acting defence secretary, Patrick Shanahan. Bolton is reported to be planning to fly to Israel for consultations on the worsening situation.

The Islamic Revolutionary Guard Corps news website said the drone “was shot down when it entered Iran’s airspace near the Kouhmobarak district in the south”, referring to the area of Iranian coast facing the strait of Hormuz.

“The downing of the American drone was a clear message to America ... our borders are Iran’s red line and we will react strongly against any aggression ... Iran is not seeking war with any country, but we are fully prepared to defend Iran,” the Revolutionary Guard commander, Hossein Salami, said, according to Iranian media. Iran has announced its intention to take the matter to the UN security council.

The US has denied the drone was anywhere near the Iranian coast and said that the use of a high-powered anti-aircraft missile was a danger to commercial airliners in the region.

“This was an unprovoked attack on a U.S. surveillance asset that had not violated Iranian airspace at any time during its mission,” General Joseph Guastella, US Central Command’s top air force commander told reporters.

“This attack is an attempt to disrupt our ability to monitor the area following recent threats to international shipping and the free flow of commerce,” Gen Guastella said. “The aircraft was over the Strait of Hormuz and fell into international waters.”

US officials confirmed the downed aircraft was a US navy Global Hawk surveillance drone, which had been hit by an Iranian surface-to-air missile over the strait of Hormuz at 11.35pm GMT.

The $130m (£102m) Global Hawk is the world’s largest surveillance drone, packed with sophisticated electronics and the size of a small commercial airliner. Iranian forces and allied militias had previously fired at and brought down US Reaper drones, but this is the biggest US target Iran has hit to date, as tensions in the region escalate.

Close to the same time as the drone was shot down, Houthi rebels in Yemen, who are backed by Iran, hit a Saudi desalination plant with an apparently sophisticated missile, and there have been a string of rocket and mortar attacks on or close to US facilities in Iraq.

On Wednesday the Pentagon confirmed it was sending an additional 1,000 troops to the Gulf in response to two attacks on commercial tankers on 13 June which the US has blamed on Iran’s Revolutionary Guard.

Trump downplayed the tanker attacks as “very minor” but US officials have made clear to Iran that it would view an attack on its forces by Iran or proxy militias as a threshold for a military response.

It is unclear how it will react to an attack on an unmanned – but very large and expensive – aircraft. Asked for comment on the agenda’s of Thursdays meeting a national security council spokesman said: “We don’t comment on internal deliberations.”

Iran said the US drone was shot down by the “3rd Khordad” air defence system, which is an Iranian equivalent to the Russian Buk system that downed Malaysia Airlines flight MH17 over Ukraine in 2014. The use of such weapons in an area of crowded skies has underlined the dangers of the standoff in the Gulf spinning out of control.

The secretary of Iran’s supreme national security council, Ali Shamkhani, had said on Wednesday that Tehran would respond to any intrusion into its airspace or waters.

Shamkhani emphasised that Iran robustly protects its aerial and maritime borders, describing its airspace as the country’s “red line”. “No matter whose plane trespasses into it, we have always given and will give a harsh response to intruders.”

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Speaking in London, the Saudi foreign minister, Adel al-Jubeir, said: “The international community is determined to push back against Iran’s aggressive behaviour”.

Saying steps were being prepared to protect shipping in the Gulf, he added: “Freedom of navigation is essential to global security and the world economy. Any attempt to close the strait of Hormuz will provoke a very strong reaction.”

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As US and Iranian forces face off in the Gulf, another potential flashpoint for conflict is drawing closer. Iran has set a deadline of 27 June by which it will breach limits on uranium stockpiles set out in the nuclear deal, a development likely to lead to renewed US demands that the EU states France, Germany and Britain join the US in pulling out of the deal.

Iran says it is gradually suspending its adherence to the deal in response to the economic stranglehold being imposed on the country by US sanctions. It has warned it will raise the level at which it enriches uranium on 8 July, which would be a much more significant step as it would considerably shorten the amount of time Iran would need to build a warhead if it were to decide to make a nuclear weapon.

A meeting of the joint commission that oversees the deal, known as the Joint Comprehensive Plan of Action, is due to meet on 28 June in Vienna – bringing together Iran, the three EU states, China, as well as Russia. The EU will urge Iran not to take further steps to pull out of the deal, and may put Iran’s actions into the JCPOA’s lengthy dispute mechanism.