The United States will destroy any Iranian drones that fly too closely to its ships and has "clear evidence" that it shot down such a drone on Thursday, a senior Trump administration official said on Friday.
"If they fly too close to our ships, they’ll continue to be shot down," the official told reporters at a briefing.
"Soon, images captured by the Guards drones from the US warship Boxer will be published to expose to world public opinion as lies and groundless the claim ... of shooting down an Iranian drone over the Strait of Hormuz," the Revolutionary Guards said in a statement carried by news agencies.
Tensions in the Gulf region mounted Thursday after Trump announced that the USS Boxer, an amphibious assault ship, "took defensive action" against the Iranian drone as it was "threatening the safety of the ship and the ship's crew."
Iranian Deputy Foreign Minister Abbas Araqchi denied on Friday that Iran had lost a drone in the Strait of Hormuz after US President Donald Trump said that a US Navy ship had "destroyed" an Iranian drone, reported news agency Reuters.
"We have not lost any drone in the Strait of Hormuz nor anywhere else. I am worried that USS Boxer has shot down their own UAS [Unmanned Aerial System] by mistake!," Araqchi said on Twitter, referring to a US warship in the strategic waterway.
First US military action
The drone shootdown comes after a series of low-level attacks in the region blamed on Tehran's forces, including placing limpet mines on several tankers and actions by what Washington calls Iranian proxies in Syria and Yemen.
Watch: US ship destroyed Iranian drone in Strait of Hormuz: President Donald Trump
In May the Pentagon announced the deployment of an aircraft carrier strike group and a bomber task force to waters near Iran in response to "indications of a credible threat by Iranian regime forces."
Tehran downed an American surveillance drone in June, prompting Trump to order airstrikes against Iran. But he called them off at the last minute, saying the plan was not "proportionate" and casualties would have been too high.
On July 4 Britain seized a fully loaded Iranian oil tanker near Gibraltar, allegedly headed for Syria in violation of sanctions.
Iran furiously branded the seizure "piracy, and one week later armed Iranian boats menaced a British tanker in the Gulf before they were driven off by a Royal Navy frigate.
That led to US calls for an international flotilla to escort hydrocarbon-laden vessels from Gulf oil fields through the Hormuz Strait.
US Central Command chief Kenneth McKenzie pledged Thursday to work "aggressively" with partners to ensure freedom of navigation in Gulf waters.
Broader conflict feared
The incidents have raised fears of a regional conflict involving the US and
its allies in the Gulf region, through which nearly a third of the world's oil is transported.
It comes amid a threatened breakdown of the 2015 Iran nuclear deal, with Washington steadily ratcheting up economically debilitating sanctions on Tehran a year after unilaterally quitting the deal.
Earlier this month Tehran purposely surpassed the deal's caps on uranium enrichment, aiming to pressure the other parties -- France, Germany, Britain, China and Russia -- to break with the US sanctions escalation and defend the economic benefits Iran was promised for agreeing to drastic limitations on its nuclear program.
On Wednesday at the United Nations in New York, Zarif accused Washington of waging "economic terrorism."
The "unlawful, extraterritorial" sanctions "represent the greatest threat to the achievement of sustainable development goals of Iran and many of our neighbours," he said.
Washington nevertheless announced fresh sanctions Thursday on what it called a "network" of companies in Iran, Belgium and China supplying crucial materials to Tehran's enrichment program.
Door open for negotiations?
Yet both sides kept open the possibility of talks. The Guardian reported Thursday that Zarif said he had offered a new deal for enhanced inspections of Iran's nuclear program if Washington agrees to remove sanctions.
Trump appeared to be receptive as well to negotiations.
He told reporters that the pressure on Iran had forced the country to reduce regional activities and suggested that could lead to negotiations.
"You look at them pulling back, and they're not pulling back because they love us. They're pulling back because they don't have money," Trump said.
"All we want to do is have a fair deal. The deal that was made was a bad deal... We can do something quickly or we can take our time. I'm in no rush."
Iran's Revolutionary Guards said on Friday they would release images to disprove US President Donald Trump's assertion that the US Navy has destroyed an Iranian drone in the Gulf.