Iran “made a very big mistake” in shooting down a US military surveillance drone, Donald Trump has said.

Tehran’s revolutionary guard claimed the attack, using a surface-to-air missile, had sent “a clear message” to the US that it was “ready for war”.

Mr Trump made the comment after quoting praise he had received on a TV news broadcast.

He tweeted: “Iran made a very big mistake!”

The US military confirmed a surveillance drone had been shot down late on Wednesday. It is thought to be either an RQ-4 Global Hawk or an MQ-4C Triton.

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The unmanned aircraft are designed to provide intelligence about huge areas of territory and opposing military forces, and aid in potential search-and-rescue missions.

Wednesday’s attack came amid heightened tensions in the region, following attacks on two tankers in the Strait of Hormuz, which Washington and its allies have blamed on Iran.

The revolutionary guard said it downed the drone over Iranian airspace, which the US disputed. General Hossein Salami said on state TV that Iran did “not have any intention for war with any country, but we are ready for war”.

Simmering tensions have raised fears that open conflict could break out, a little over a year after Mr Trump withdrew the US from the so-called Iran nuclear deal in favour of economic sanctions.

Tehran has said it now plans to increase uranium enrichment activities, and it is expected to breach the limits imposed under the 2015 nuclear agreement by 27 June.

Iran’s foreign minister, Javad Zarif, tweeted that the US had encroached on Iranian territory with the drone and that Tehran would “zealously defend” the nation’s “skies, land and water”.

He has accused the US of “lying” about the fact the drone was shot down in international waters and claimed Tehran would take its evidence to the UN to prove it.

Washington has beefed up its military presence in the region with additional troops and the aircraft carrier USS Abraham Lincoln, alongside its strike group of five destroyers and a guided missile cruiser. Mr Trump’s national security adviser, John Bolton, who is known for pushing hardline policies about how to deal with Iran, is also travelling to Israel to discuss “regional security”, according to the White House.

Brian Hook, the US State Department’s special representative for Iran, has been sent to the Gulf to clarify the Trump administration’s position on Tehran to allies in the region.

In front of congress yesterday, Mr Hook would not rule out the possibility that the White House might justify a military confrontation with Iran using the 2001 law that authorised the Afghanistan war.

However, he added that the Trump administration was “not seeking military action”.

The Authorisation for Use of Military Force (AUMF) – the law Mr Hook was referring to – was passed by congress on 14 September 2001 after the 9/11 attacks.

It is generally interpreted as giving congressional authorisation for US military action in Afghanistan, as well as against al-Qaeda and affiliates.

New York representative Eliot Engel, who chairs the House Foreign Affairs Committee, was among those who pushed Mr Hook on the possible use of AUMF during the hearing on Wednesday.

“I see a growing risk of miscalculation,” the Democrat said.

Mr Hook added: “If the use of military force is necessary to defend US national security interests, we will do everything that we are required to do with respect to congressional war powers and we will comply with the law.”

He said the Trump administration’s Iran policy was ultimately aimed at a compromise deal on the nuclear issue and sanctions.

“No one should be uncertain about our desire for peace or our readiness to normalise relations should we reach a comprehensive deal,” he said.

Iran shoots down US military drone with surface-to-air missile

Mr Hook did not rule out the possibility of the situation escalating into conflict, but said Washington was not currently thinking that way. “There is no talk of offensive action. It’s a defensive move.”

Senior Republican Lindsey Graham, a Trump ally who sits on the Senate foreign relations committee, said that he had spoken to the president and “he believes that we’re getting into a bad space, that his options are running out”.

Addressing reporters in the wake of Mr Trump’s latest tweet, Mr Graham said that he told the president: “You need to tell the Iranians that if they increase their enrichment for uranium that would be a provocative act towards the United States and Israel.”