Oil prices have increased as high as 4 percent since the explosions.
The incident comes after the United States alleged that Iran used mines to attack four oil tankers off the nearby Emirati port of Fujairah last month. He didn't elaborate and took no questions.
Katada's account partly contradicted American allegations of a mine attack, but did mention that the crew had spotted an Iranian Navy ship nearby. Iranian officials have rejected the accusation.
"Facts must be established and responsibilities clarified", he said.
But the latest incident has increased fears that tensions could lead to a possible military confrontation between the U.S. and Iran.
Two oil tankers near the strategic Strait of Hormuz were reportedly attacked today. He dismissed the USA claims as "baseless". Iran's oil exports have dropped to around 400,000 barrels per day in May from 2.5 million barrel per day in April previous year.
Urban said in a statement the attacks "are a clear threat to worldwide freedom of navigation and freedom of commerce".
"That the U.S. immediately jumped to make allegations against Iran-w/o a shred of factual or circumstantial evidence-only makes it abundantly clear that the #B_Team is moving to a #PlanB: Sabotage diplomacy-including by @AbeShinzo-and cover up its #EconomicTerrorism against Iran", Zarif tweeted.
Katada said the Kokuka Courageous's crew saw flying objects approaching the ship. The Bahrain-based U.S. Navy Fifth Fleet said it had assisted the two tankers after receiving distress calls.
The U.S. planned to raise the attacks at the U.N. Security Council later Thursday.
Kuwait's United Nations ambassador, Mansour Al-Otaibi, president of the council for June, said after the meeting that all 15 council members had condemned the attacks.
Pompeo told journalists on Thursday that the United States assessment of Iran's involvement was based in part on intelligence, as well as the expertise needed for the operation.
Washington's view was not shared by other council members, who noted that there was no clear evidence to link Iran to the attacks, diplomats said.
World oil prices surged following reports of the suspected attacks, exacerbating tensions in the crude-rich Middle East, analysts said.
"The United States will defend its forces, interests and stand with our partners and allies to safeguard global commerce and regional stability", Mr Pompeo said, noting that Iran had previously threatened to curtail oil transport in the Strait of Hormuz.
"However, regarding what you mentioned about the President of the USA, I do not consider Trump as a person worth exchanging any message with and I have no answer for him, nor will I respond to him in the future", Khamenei reportedly said in response.
"Tension across the Middle East is high - and the attacks on two tankers have further exacerbated the situation, even though there does not appear to have been any damage to the cargos", John Hall, chairman of British-based consultancy Alfa Energy, said. Japanese public broadcaster NHK, citing Kokuka Sangyo's chief executive officer, said the ship was hit by a shell. "If the waters are becoming unsafe, the supply to the entire Western world could be at risk", said Paolo d'Amico, chairman of INTERTANKO tanker association.
And though details of what happened were still scarce, the incidents came amid heightened frictions between the United States and Iran.
Pompeo speculated in his address this morning that Iran is "lashing out, because the regime wants our successful maximum pressure campaign lifted". 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. Abe, whose country was a big importer of Iranian oil until Trump ratcheted up sanctions, urged all sides not to let tensions increase.
Khamenei also said Iran remained opposed to building atomic weapons, but offered a challenge to Trump.