Washington/Dubai, April 14 -- The US military said it will begin a blockade of ships leaving Iran's ports on Monday, and Tehran threatened to retaliate against ports of its Gulf neighbours, after weekend talks failed to reach a deal to end the war, leaving a ceasefire in jeopardy. Oil prices surged when trade reopened on Monday, with no sign of a swift reopening of the Strait of Hormuz to ease the worst ever disruption in supplies. Since the war started, Iran has effectively shut the strait to all vessels except its own, saying ships would only be allowed through under Iranian control and subject to a fee. US President Donald Trump said he would now block Iran's ships too, and any vessels that paid Iran a toll. The ceasefire that halted six weeks of US and Israeli airstrikes is under threat, with only a week left to run, after Washington said Tehran had rejected its demands at talks in Islamabad, the highest-level discussions since Iran's 1979 Islamic Revolution. The US military's regional Central Command said the blockade would start at 10 am ET on Monday, "enforced impartially against vessels of all nations entering or departing Iranian ports and coastal areas, including all Iranian ports on the Arabian Gulf and Gulf of Oman". The US military said it will enforce a blockade in the Gulf of Oman and Arabian Sea east of the Strait of Hormuz and it will apply to all vessel traffic regardless of flag, the U.S. Central Command said in a note to seafarers seen by Reuters. "Any vessel entering or departing the blockaded area without authorization is subject to interception, diversion, and capture," the note said. "The blockade will not impede neutral transit passage through the Strait of Hormuz to or from non-Iranian destinations." Two Iranian-linked tankers, the Aurora and New Future, laden with oil products and diesel, left the strait on Monday shortly before the US blockade was due to take effect, according to data from provider LSEG. An Iranian military spokesperson, quoted by state media, said any US restrictions on vessels in international waters would be illegal and amount to "piracy". If Iranian ports were threatened, no port in the Gulf or Gulf of Oman would remain secure, the spokesperson said. Earlier, Iran's Revolutionary Guards said any military vessels approaching the strait would be considered to have violated the ceasefire. On Sunday, Trump had posted on social media: "No one who pays an illegal toll will have safe passage on the high seas," adding, "Any Iranian who fires at us, or at peaceful vessels, will be BLOWN TO HELL!" "Trump wants a quick fix," said Dana Stroul, a former senior Pentagon official during the Biden administration now at The Washington Institute for Near East Policy. "The reality is, this mission is difficult to execute alone and likely unsustainable over the medium to long term." With the war unpopular at home and rising energy prices causing political blowback, Trump paused the US-Israeli bombing campaign last week after threatening to destroy Iran's "whole civilisation" unless it reopened the strait. Iran has effectively ignored that demand, while bringing new demands of its own to the talks, including recognition of its control of the strait, the lifting of all sanctions and the withdrawal of forces from the huge US military bases across the Middle East. Trump has declared victory, despite failing so far to achieve the objectives he set out at the start of the war: to eliminate Iran's ability to strike its neighbours, end its nuclear programme and make it easier for Iranians to topple their government. Iran retains missiles and drones that can hit Gulf neighbours, and a stockpile of uranium enriched to near bomb-making levels that the UN nuclear agency estimated last year at more than 400kg. Tehran's leadership, which faced a popular uprising at the start of the year, has withstood the US onslaught with no sign of organised opposition. US officials said Iran had rejected demands at the talks to give up the uranium stockpile, end future enrichment and halt funding for its regional allies, positions carried over from negotiations Trump abandoned two days before the war. Washington still hopes that Iran will seek peace and a chance to begin rebuilding from damage that has deepened an economic crisis that provoked pre-war domestic unrest. But emboldened Iranian officials say they are in a stronger position than before, and will make a deal only if the US makes further concessions. Iran had "encountered maximalism, shifting goalposts, and blockade" from the United States at the talks, said Foreign Minister Abbas Araqchi. "Zero lessons learned," he added. "Good will begets good will. Enmity begets enmity." Benchmark oil prices, which had eased last week after the ceasefire was announced, surged more than 7% on Monday, back above $100 a barrel as traders digested the news that the weekend talks had failed to produce a breakthrough....