US President Donald Trump on Thursday said Iran made "a very big mistake" by shooting down a US military drone that Tehran said was on a spy mission over its territory, in an incident that fanned fears of wider military conflict in the Middle East.
The United States, which called the event an "unprovoked attack" in international air space, is pursuing a campaign to isolate Iran to contain its nuclear and ballistic missile programs and limit its role in regional wars.
It was the latest in an escalating series of incidents in the Gulf region, a critical artery for global oil supplies, since mid-May including explosive strikes on six oil tankers as Tehran and Washington have edged toward confrontation.
"Iran made a very big mistake!" Trump said in a Twitter post.
It was unclear how the United States might respond and US House of Representatives Speaker Nancy Pelosi, the top Democrat in Congress, said Washington had no appetite for war with Iran.
Iran has denied involvement in the tanker attacks, but global jitters about a new Middle East conflagration disrupting oil exports have triggered a jump in crude prices. They surged by more than US$3 to above US$63 a barrel on Thursday.
Saudi Arabia, Washington's main gulf ally, said Iran had created a grave situation with its "aggressive behavior" and the kingdom was consulting other Gulf Arab states on next steps.
"When you interfere with international shipping it has an impact on the supply of energy, it has an impact on the price of oil which has an impact on the world economy. It essentially affects almost every person on the globe," Adel al-Jubeir, Saudi minister of state for foreign affairs, told reporters in London.
Tensions flared with Trump's withdrawal last year from world powers' 2015 nuclear accord with Iran and have worsened as Washington imposed fresh sanctions to throttle Tehran's vital oil trade. Iran retaliated earlier this week with a threat to breach limits on its nuclear activities imposed by the deal.
Upping the ante, Washington said on Monday it would deploy about 1000 more troops, along with Patriot missiles and manned and unmanned surveillance aircraft, to the Middle East on top of a 1500-troop increase announced after the May tanker attacks.
Iranian state media said the "spy" drone was brought down over the southern Iranian province of Hormozgan, which is on the Gulf, with a locally made "3 Khordad" missile.
A US official said the drone, formally called an RQ-4A Global Hawk High-Altitude, Long, Endurance Unmanned Aircraft System, had been downed in international air space over the Strait of Hormuz, through which about a third of the world's seaborne oil exits the Gulf..
Navy Captain Bill Urban, a spokesman for the US military's Central Command, said Iran's account that the drone had been flying over Iranian territory was false.
"This was an unprovoked attack on a US surveillance asset in international air space," Urban said. The drone, he added, was downed over the Strait of Hormuz at approximately 2335 GMT - in the early morning hours of local time in the Gulf.
Separately, a US official told Reuters on condition of anonymity the debris field from the drone was in international waters in the Strait and US naval assets have been dispatched to the area.
Iran's foreign ministry said the drone had violated Iranian air space and warned of the consequences of such "illegal and provocative" measures.
Independent confirmation of the drone's location when it was brought down was not immediately available.
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.
Iranian 'red line'
"Our air space is our red line and Iran has always responded and will continue to respond strongly to any country that violates our air space," Ali Shamkhani, secretary of the Supreme National Security Council, told Iran's Tasnim news agency.
The RQ-4A's manufacturer, Northrop Grumman, says on its website that it can fly for over 24 hours at a time at altitudes higher than 16km, with an operational range of 8200 nautical miles.
The Trump administration sought on Wednesday to rally global support for its pressure on Iran by displaying limpet mine fragments it said came from an oil tanker damaged in the June 13 attacks, saying the ordinance closely resembled mines publicly displayed in Iranian military parades.
European diplomats have said more evidence is needed to pinpoint responsibility for the tanker strikes.
The US sanctions net draped over Iran, scuttling its oil exports and barring it from the dollar-dominated global finance system, have hammered Iran's economy, undoing the promise of trade rewards from the 2015 deal to curb its nuclear ambitions.
Trump has sent forces including aircraft carriers, B-52 bombers and troops to the Middle East over the past few weeks. Iran said last week it was responsible for the security of the Strait of Hormuz, calling on American forces to leave the Gulf.
Tehran has also said it will shortly suspend compliance with the nuclear deal's curbs on its uranium enrichment, meant to block any pathway to nuclear weapons capability, and threatened to disrupt oil shipments through the Strait of Hormuz.
But Trump - who sees the nuclear deal as flawed to Iran's advantage and requiring renegotiation - and Iranian Supreme Leader Ayatollah Ali Khamenei have both said they have no interest in starting a war.