Iran has broadcast footage it says disproves US claims to have destroyed an Iranian drone in the Gulf.
Iranian state TV says it shows warships in the strategic Strait of Hormuz, and was filmed by the same drone after the time the US said it had been downed.
Despite the denials from Iran, US President Donald Trump said he had "no doubt" the drone had been taken down.
In a separate development, Iranian state media said Iran had seized a British-flagged oil tanker in the Gulf.
Reports said the Stena Impero vessel was captured by the Iranian Revolutionary Guard for "violating international regulations".
The owners of the Stena Impero, which was bound for Saudi Arabia, said they had been unable to contact the vessel, which had 23 personnel on board and was "heading north towards Iran".
Tensions between the US, the UK and Iran remain high, after a series of incidents in the world's key shipping area.
In June, Iran shot down a US military drone in the same area. Iran has also been blamed by the US for a number of attacks on tankers since May - allegations Tehran denies.
The incidents have triggered fears of a military conflict in the region.
What does the Iranian video purportedly show?
The video shows black and white aerial views of warships moving in water, indicating the time, the date and the geographical co-ordinates.
Iranian state TV said it was taken by the drone alleged to have been downed, as it flew over an American amphibious group led by the USS Boxer - the navy ship in question.
Iran's Islamic Revolutionary Guard Corps (IRGC), who published the footage, said it was taken "before and even after the time Americans claim" to have destroyed their drone.
But the pictures are inconclusive, says the BBC's diplomatic correspondent Paul Adams.
He says at least some of the images appear to have been filmed from an Iranian helicopter that was also on the scene.
According to a Wall Street Journal reporter on board the USS Boxer at the time, an Iranian Bell 212 helicopter was flying "yards away" from the vessel before being chased off by American helicopters.
What does the US say happened?
President Trump said the US Navy was forced into action after the drone came within 1,000 yards (914m) of a US warship on Thursday.
Mr Trump said the USS Boxer "took defensive action" against the Iranian aircraft as it was "threatening the safety" of the navy amphibious assault ship and its crew early on Thursday.
"The drone was immediately destroyed... after ignoring multiple calls to stand down," he added.
According to the Pentagon, the ship was in international waters when the drone approached at 10:00 local time (05:30 GMT).
Iran was quick to dismiss President Trump's claim, with one senior official even suggesting it may have targeted its own drone by mistake.
"I am worried that USS Boxer has shot down their own (drones) by mistake!" Iran's Deputy Foreign Minister Abbas Araqchi tweeted on Friday.
After the alleged footage was released by Iran, President Trump told reporters he was confident US forces had "shot down" the drone.
Why all the tension?
It's not the first time the US and Iran have been at odds over an incident in the strategic sea passage in the Gulf.
Last month, Iran shot down a US surveillance drone over the Strait of Hormuz, accusing it of violating Iranian airspace. But the US military said the drone had been over international waters at the time, and condemned it as an unprovoked attack.
Tensions between the two nations have risen sharply since the US tightened sanctions it reimposed on Iran's oil sector after unilaterally withdrawing from a landmark 2015 nuclear deal.
The US has also called on Iran to release a Panamanian-flagged Riah tanker and 12 of its crew, which was seized by the Revolutionary Guards on Sunday during a naval patrol.
Iran says the vessel had been smuggling fuel, and released footage of Iranian speedboats circling around it.
The US has blamed Iran for two separate attacks on oil tankers in the Gulf of Oman in May and June - an allegation Tehran has denied.
In July, Iranian boats tried to impede a British oil tanker near the Gulf - before being driven off by a Royal Navy ship, the Ministry of Defence said.
UK warships have also been shadowing British oil tankers in the area since Iran threatened to seize one in response to the impounding of an Iranian tanker off Gibraltar earlier this month.
The UK said the tanker was suspected of breaching EU sanctions against Syria. Iran denied it was headed there.