Iran has accused the US of “warmongering” and rejected claims it damaged two oil tankers in the Gulf of Oman.
Iranian officials said the claim made by US Secretary of State Mike Pompeo that Iran was responsible was “unfounded”.
Mr Pompeo said the US made its assessment based on intelligence about the type of weapons used.
And the US military's Central Command later said there is video evidence of Iranian forces removing an unexploded limpet mine from one of the two ships.
But responding to the claims, the Iranian mission to the United Nations said in a statement that Iran "categorically rejects the US unfounded claim with regard to 13 June oil tanker incidents and condemns it in the strongest possible terms.”
It accused the United States and its regional allies, which include Iranian rival Saudi Arabia and the United Arab Emirates, of "warmongering."
Iran called on "the international community to live up to its responsibilities in preventing the reckless and dangerous policies and practices of the U.S. and its regional allies in heightening the tensions in the region."
Mr Pompeo earlier said that the ships were targeted as part of a "campaign" of "escalating tension" by Iran and a threat to international peace and security.
The tankers came under suspected attack in the early hours of today near the strategic Strait of Hormuz, with one of them set ablaze.
Dozens of sailors were evacuated after explosions on the MT Front Altair and the Kokuka Courageous.
The US Navy said one oil tanker was adrift and on fire, and it was assisting the tankers after receiving two distress calls
Each was loaded with petroleum products, and the Front Altair burned for hours, a fire that charred half of one of the vessel's sides and sent up a column of thick, black smoke.
"It is the assessment of the United States government that the Islamic Republic of Iran is responsible for the attacks that occurred in the Gulf of Oman today."
He added: "This assessment is based on intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping, and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophisticatiom."
The suspected attacks occurred about 40 kilometres (25 miles) off the southern coast of Iran.
The Norwegian-owned Front Altair, loaded with naphtha from the United Arab Emirates, radioed for help as it caught fire.
A short time later, the Japanese-owned Kokuka Courageous, loaded with methanol from Saudi Arabia and Qatar, also called for help.
The US Navy sent a destroyer, the USS Bainbridge, to assist, said Cmdr Joshua Frey, a 5th Fleet spokesman. He described the ships as being hit in a "reported attack," without elaborating.
Frontline, the firm that operates the Front Altair, told The Associated Press that an explosion was the cause of the fire.
Its crew of 23 - from Russia, the Philippines and Georgia - was safely evacuated to the nearby Hyundai Dubai vessel, it said.
BSM Ship Management said the Kokuka Courageous sustained hull damage and its 21 Filipino sailors had been evacuated, with one suffering minor injuries.
All 21 were placed aboard the Bainbridge, according to Lt Col Earl Brown, a spokesman for the US Central Command.
Earlier, Iranian state television said 44 sailors from the two tankers were transferred to an Iranian port in the southern province of Hormozgan.
Downing Street called the suspected attacks "completely unacceptable" and said the UK is ready to assist in any rescue or investigation.
Theresa May's official spokesman told a Westminster briefing: "Attacks on civilian vessels like these are completely unacceptable.
"It's vital that freedom of navigation is respected and observed.
"We are in contact with international partners and are ready to assist in any rescue effort or investigation."