US President Donald Trump said his country’s military have begun blockading Iranian ports in an effort to force Tehran to open the strategic Strait of Hormuz and accept Washington’s terms to end the war that has been raging since 28 February.At least two tankers approaching the Strait late on Monday turned around, according to a post on X by vessel tracker MarineTraffic, who announced the development shortly after the US Navy began its blockade.The UK Maritime Trade Operations agency said the blockade restricted “the entirety of the Iranian coastline, including ports and energy infrastructure.”Its notice to mariners said transit through the strait to or from non-Iranian places was not reported to be impeded though ships “may encounter military presence.”“We can’t let a country blackmail or extort the world because that’s what they’re doing,” Trump said of Iran at the White House, where he announced the blockade had started.He suggested the US remains willing to engage with Iran. “I can tell you that we’ve been called by the other side,” Trump said, adding that “they want to work a deal.”Discussions between Washington and Iran about a second round of in-person negotiations are underway, according to two US officials and a person familiar with the matter.A diplomat from one of the mediating countries – Pakistan, Turkey and Egypt – said Tehran and the US have agreed to more talks.Iran’s effective closure of the strait, through which a fifth of global oil transits in peacetime, has sent oil prices skyrocketing, pushing up the cost of gasoline, food and other basic goods far beyond the Middle East.Before the US blockade, Tehran had allowed some ships perceived as friendly – flagged by countries not allied with the US or Israel – to pass, while charging considerable fees, leading to accusations it is holding the global economy hostage.Some analysts are doubtful that the United States can restore normal shipping through sheer force alone. It’s not clear how the blockade will work or what the dangers might be to US forces if Trump decides to put boots on the ground to reopen the strategic waterway.Iran responded with threats on all ports in the Persian Gulf and the Gulf of Oman, taking aim at US-allied countries.“Security in the Persian Gulf and the Sea of Oman is either for everyone or for NO ONE,” the Islamic Republic of Iran Broadcasting reported Monday. “An Iranian military statement said: “NO PORT in the region will be safe.”Washington’s blockade and Iran’s threatened retaliation set up an extraordinary showdown that posed serious risks for the global economy and raised the spectre that the ceasefire could collapse and the fighting could resume.The US president late on Monday again reiterated claims that the US military had “obliterated” Iran’s Navy, noting that 158 ships were completely destroyed and are “laying at the bottom of the sea”.“What we have not hit are their small number of, what they call, “fast attack ships,” because we did not consider them much of a threat. Warning: If any of these ships come anywhere close to our BLOCKADE, they will be immediately ELIMINATED, using the same system of kill that we use against the drug dealers on boats at Sea.”The ongoing two-week ceasefire between the US, Israel and Iran was meant to reopen the strait of Hormuz to maritime traffic in an effort to bring global crude prices down, after it had soared to well above $100 (€85) a barrel for weeks.As shipping remains limited, and with the introduction of the US blockade now, Brent crude, the international standard, has been slowly rising from its six-week low of $91 (€77) a barrel on 8 April, trading at just over $98 (€83) on Tuesday morning.