Iran says it "categorically rejects" US claims that it is behind attacks on two oil tankers in the Gulf of Oman.
US Secretary of State Mike Pompeo had blamed Iran for the "unprovoked attacks" on Thursday.
He added that the US had made its assessment based on intelligence about the type of weapons used.
But Iran dismissed the claim as "unfounded". A senior Iranian official had earlier told the BBC that "Iran has no connection" with the explosions.
Dozens of crew members were rescued after the blasts on the Japanese-owned Kokuka Courageous and the Front Altair, owned by a Norwegian company.
In a statement released on Friday, the Iranian mission to the United Nations said: "Iran categorically rejects the US unfounded claim with regard to 13 June oil tanker incidents, and condemns it in the strongest possible terms."
Within hours of the denial, the US military's Central Command released a video it says shows Iran's Revolutionary Guard "removing [an] unexploded limpet mine" from the side of the Kokuka Courageous following the blasts.
The blasts come a month after four oil tankers were damaged in an unclaimed attack off the United Arab Emirates. The US at the time blamed Iran - but Tehran denied the accusations.
Oil prices jumped as much as 4% after Thursday's incident in the Gulf of Oman, which lies at one end of a vital shipping lane through which hundreds of millions of dollars of oil pass.
BIMCO, the world's largest international shipping association, said the tension in the area are "now as high as it gets without being an actual armed conflict".
Meanwhile, UK Foreign Secretary Jeremy Hunt warned that if Iran was involved, "it is a deeply unwise escalation which poses a real danger to the prospects of peace and stability in the region".