Iran’s shooting down of a US drone took place in international airspace and was an “unprovoked attack”, the American military has said.

A statement from Central Command (Centcom) said the unmanned aircraft – a RQ-4A Global Hawk maritime surveillance drone – was “shot down by an Iranian surface-to-air missile system while operating in international airspace over the Strait of Hormuz” early on Thursday.

The statement added that “Iranian reports that the aircraft was over Iran are false” and that “this was an unprovoked attack on a US surveillance asset in international airspace”.

Iran’s paramilitary Revolutionary Guard, which answers to Supreme Leader Ayatollah Ali Khamenei, said it shot the drone down on Thursday morning when it entered Iranian airspace near the Kouhmobarak district in southern Iran’s Hormozgan province.

Iranian supreme leader
The Revolutionary Guard answers to the Supreme Leader Ayatollah Ali Khamenei (Office of the Iranian Supreme Leader/AP)

The US military previously alleged that Iran had fired a missile at another drone last week that was responding to the attack on two oil tankers near the Gulf of Oman.

The attacks come against the backdrop of heightened tensions following US President Donald Trump’s decision to withdraw from Tehran’s nuclear deal a year ago.

Iran has quadrupled its production of low-enriched uranium and threatened to boost its enrichment closer to weapons-grade levels, in a bid to pressure Europe for new terms to the 2015 nuclear deal.

Separately, Saudi Arabia said on Thursday that Yemen’s Iranian-allied Houthi rebels had launched a rocket targeting a desalination plant in the kingdom on Wednesday night. The White House said Mr Trump had been briefed about that attack.

In recent weeks, the US has sent an aircraft carrier to the Middle East and deployed additional troops alongside the tens of thousands already in the region. From Yemen, the Houthis have launched bomb-laden drones into neighbouring Saudi Arabia.

All this has raised fears that a miscalculation or further rise in tensions could push the US and Iran into an open conflict, some 40 years after Tehran’s Islamic Revolution.

Thursday’s drone incident marks the first direct Iranian-claimed attack on the US amid the crisis.

“We do not have any intention for war with any country, but we are fully ready for war,” Revolutionary Guard commander General Hossein Salami said in a televised address.

Iran’s Revolutionary Guard commander General Hossein Salami
General Hossein Salami (Sepahnews via AP)

The Revolutionary Guard said it shot the drone down at 4.05am after it collected data from Iranian territory, including the southern port of Chahbahar near Iran’s border with Pakistan.

Iran used its air defence system, known as Third of Khordad, to shoot down the drone — a truck-based missile system that can fire up to 18 miles (30 kilometres) into the sky, the semi-official Fars news agency reported.

The US has been worried about international shipping through the Strait of Hormuz – the narrow mouth of the Persian Gulf through which 20% of all global oil moves – since the limpet mine attacks in May and June.

Speaking to a crowd in the western city of Sanandaj, General Salami described the American drone as “violating our national security border”.

“Borders are our red line,” General Salami said. “Any enemy that violates the borders will be annihilated.”

Iran’s Foreign Ministry separately protested the drone, saying it had entered Iranian territory.

Speaking during a televised call-in show on Thursday, Russian President Vladimir Putin warned the US against using force on Iran, saying it would have catastrophic consequences.

Mr Putin said US military action against Iran would be a “catastrophe for the region as a minimum”.

He added that it would trigger an escalation of hostilities with unpredictable results.

Mr Putin said that Iran had abided by the terms of a nuclear deal despite the US withdrawal, adding that he considered American sanctions against Iran unfounded.

Meanwhile, Mr Trump tweeted on Thursday that “Iran made a very big mistake” in shooting down a US drone.

White House press secretary Sarah Sanders said Mr Trump was briefed on Wednesday night and again on Thursday morning about the incident.

She said the administration would also keep in touch with lawmakers on Capitol Hill.