US President Donald Trump blamed Iran on Friday for attacks on two oil tankers at the entrance to the Gulf despite Tehran's denials, raising fears of a confrontation in the vital oil shipping route.Iran has dismissed earlier US charges that it was behind Thursday's attacks that crippled two tankers. It has previously suggested it could block the Strait of Hormuz, the main route out for Middle Eastern oil, if its own exports were halted.The blasts followed similar attacks a month earlier on four tankers, which Washington also blamed on Tehran.They come at a time of escalating tension between the two countries. Last month the United States sharply tightened economic sanctions against Iran, which in response has threatened to step up its nuclear activity.“Iran did do it and you know they did it because you saw the boat,” Trump told Fox News.He was referring to a video released on Thursday by the US military which said it showed Iran's Revolutionary Guards were behind the blasts that struck the Norwegian-owned Front Altair and the Japanese-owned Kokuka Courageous in the Gulf of Oman, at the mouth of the Gulf.Iran said the video proved nothing and that it was being made into a scapegoat. "These accusations are alarming," Foreign Ministry spokesman Abbas Mousavi said.Iran has accused the United States and its regional allies such as Saudi Arabia and the United Arab Emirates of "warmongering" by making accusations against it.Asked how he planned to address Tehran and prevent any further incidents, Trump told Fox News: "We're going to see." He also said any move to close the Strait of Hormuz would not last long.Nevertheless, Trump, who last year pulled the United States out of an agreement between world powers and Tehran to curb Iran's nuclear program in return for the lifting of sanctions, said that he was open to negotiations with Iran.Iran has repeatedly said it will not re-enter talks with the United States unless it reverses Trump's decision to withdraw from the nuclear deal.Tehran and Washington have both said they have no interest in starting a war. But this has done little to assuage concerns that the two arch foes could stumble into a conflict.OIL, INSURANCEOil prices rose about 1% on Friday, reflecting the jitters. Insurance costs for ships sailing through the Middle East have jumped by at least 10% after the attacks, ship insurers said.UN Secretary-General Antonio Guterres called on Friday for an independent investigation of the attacks. He told the UN Security Council on Thursday the world cannot afford "a major confrontation in the Gulf region."The tanker attacks took place while Prime Minister Shinzo Abe of Japan - a big buyer of Iranian oil until it was forced by the new US sanctions to stop - was visiting Tehran on a peacemaking mission, bringing a message from Trump.Iran dismissed Trump's message, details of which were not made public. "I do not see Trump as worthy of any message exchange, and I do not have any reply for him, now or in future," Iranian Supreme Leader Ali Khamenei said.Trump and Abe discussed the oil tanker attacks in a phone call on Friday, the White House said.The US military said black-and-white footage it filmed from a US aircraft showed Iran's Guards on a patrol boat drawing up to the Kokuka Courageous and removing an unexploded limpet mine from its hull.The Japanese-owned tanker, abandoned by its crew, was being towed to a port in the United Arab Emirates on Friday, after a Dutch firm said it had been appointed to salvage the ships.The second tanker, the Front Altair, which was set ablaze by a blast, was still languishing at sea, although the fire that had charred the hull had been put out.Iranian military fast-boats in the Gulf of Oman were preventing two privately owned tug boats from towing away the Front Altair, a US official said on Friday.China, the European Union and others have called for restraint from all sides. In a notable signal that close US allies are wary of Washington's position, Germany said the US video was not enough to apportion blame for Thursday's attack.Last month Washington scrapped waivers that had allowed some countries to continue importing Iranian oil, effectively ordering all countries to blacklist Iran or face sanctions themselves.Iran's crude exports fell to about 400,000 barrels per day (bpd) in May from 2.5 million bpd in April 2018, starving Iran's economy of its main source of revenue.Iran says it is still abiding by the terms of the nuclear deal, but cannot do so indefinitely unless it receives some of the economic benefits that were promised. Last month it said it would boost enrichment of uranium, a move that could potentially lead to it building up a stockpile prohibited under the deal.Washington has also blamed Iran or its proxies for attacks on May 12 that crippled four oil tankers in the same area, and has said Tehran was behind May 14 drone strikes on two Saudi oil-pumping stations. Tehran has denied all those charges.There have been conflicting accounts of the cause of Thursday's blasts. An initial report that Kokuka Courageous was struck by a torpedo was dismissed by a source familiar with the issue. The owner of the tanker, which carried methanol, later said it was hit by two "flying objects."Iranian TV showed 23 crew in Iran believed to be from Front Altair on Friday, and said its experts would assess whether they could return to the ship. The crew from Kokuka Courageous were picked up and handed to a US Navy ship on Thursday.The Trump administration said in May it would send troops and other forces to the Middle East, citing Iranian threats, a move Tehran has called "psychological warfare."The administration argues that the 2015 nuclear deal, negotiated under Trump's predecessor Barack Obama, was too limited, and says re-imposing sanctions will force Tehran back to the table to make more concessions.Most US allies in Europe and Asia disagree and say pulling out of the deal was a mistake that will empower hardliners in Iran and hurt the pragmatic faction that promised Iranians economic benefits in return for opening up to the world.