A US military drone has been shot down by an Iranian missile near to the country's airspace.
Unnamed US officials quoted by Reuters and AP news agencies said the intelligence drone was downed in international airspace over the Strait of Hormuz, south of Iran.
This contradicts reports by Iran's state-run IRNA news agency which said the country's Revolutionary Guard had shot down an American drone in its airspace
One of the items recovered by the US Navy from the Japanese-owned Kokuka Courageous
IRNA said the drone was hit when it entered Iranian airspace near the Kouhmobarak district in southern Iran's Hormozgan province.
Citing the paramilitary Revolutionary Guard, IRNA identified the drone as an RQ-4 Global Hawk, a high-altitude, long-endurance unmanned aircraft designed to provide intelligence, surveillance and reconnaissance.
Navy Captain Bill Urban, a US Central Command spokesman, earlier denied the reports.
"No US aircraft were operating in Iranian airspace today," he said.
White House spokeswoman Sarah Sanders said President Donald Trump had been "briefed on the reports of a missile strike in the Kingdom of Saudi Arabia".
"We are closely monitoring the situation and continuing to consult with or partners and allies," she added.
It comes a day after Washington announced it was sending another 1,000 troops to the Middle East in response to what it described as "hostile behaviour" by Iranian forces.
The US has blamed Iran for attacks on tankers and cargo ships in the Gulf of Oman and Strait of Hormuz, a major transit route for global oil supplies.
On Wednesday the US navy released pictures of pieces of mines recovered after the attacks which it said "strikingly" resemble those belonging to Iran.
Officials showed debris and a magnet recovered, they said, from the tanker Kokuka Courageous to reporters at the US navy's 5th Fleet base near Fujairah, in the United Arab Emirates (UAE).
Iran's Revolutionary Guard left them behind when they removed an unexploded limpet mine after the attack, the officials claimed.
Tehran has denied any involvement.
Tensions between the two countries have increased since Mr Trump last year withdrew America from the 2015 international nuclear deal and reimposed sanctions on Iran.
Iran has threatened to pull out of its commitments under the Obama-era agreement and increase its uranium enrichment to 20% if new and better terms with world powers are not reached on its nuclear programme.
Iranian President Hassan Rouhani issued the 60-day ultimatum to the remaining signatories of the nuclear deal - Britain, China, the European Union, France and Germany - in May.
The 2015 deal limits Iran to enriching uranium to 3.67%, which can fuel a commercial nuclear power plant.
Weapons-grade uranium needs to be enriched to around 90%.