The United States military began implementing a naval blockade of the Strait of Hormuz on Monday, sharply escalating tensions with Iran after weekend peace talks in Islamabad collapsed without a deal and threatening to unravel a fragile ceasefire that has held for roughly two weeks. US Central Command (CENTCOM) announced that its forces would block all maritime traffic entering and exiting Iranian ports and coastal areas starting at 10am Eastern Time (1400 GMT), while specifying it would "not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports." The announcement caused all traffic through the strait to stop, according to shipping intelligence firm Lloyd's List — a dramatic halt for a waterway that, in normal times, handles up to 140 vessel transits per day and carries roughly a fifth of the world's crude oil supply.

The blockade came hours after the first round of direct US-Iran negotiations — held in Islamabad and mediated by Pakistan — ended without agreement. Senior delegations led by US Vice President J.D. Vance, alongside special envoys Steve Witkoff and Jared Kushner, and Iran's Parliamentary Speaker Mohammad Bagher Ghalibaf and Foreign Minister Abbas Araghchi had discussed a broad agenda including the nuclear file, sanctions relief, war reparations, and the status of the strait itself. The talks broke down over deep structural disagreements: Washington demanded an open-ended prohibition on uranium enrichment and "unrestricted navigation" through Hormuz, while Tehran insisted on full sanctions relief before making concessions and maintained that control over the strait — which it considers to lie under the joint territorial sovereignty of Iran and Oman — was a non-negotiable red line. Both sides nonetheless left the door open to further talks, with Pakistani officials describing the engagement as "substantive rather than symbolic."

Iran's response to the blockade announcement was swift and defiant. Ghalibaf, returning to Tehran, declared: "If they fight, we will fight, and if they come forward with logic, we will deal with logic. We will not bow to any threats." Iran's Revolutionary Guard warned that "approaching military vessels to the strait of Hormuz is considered a violation of the ceasefire." President Trump, for his part, said he was unconcerned about whether Iran returned to talks. "I don't care if they come back or not. If they don't come back, I'm fine," he told reporters. The Wall Street Journal reported that Trump and his advisers were also considering resuming limited military strikes against Iran.

Global markets reacted immediately. Brent crude oil — the international benchmark — surged more than 8% to above $102 a barrel, while US West Texas Intermediate rose to over $104. Oil had already climbed from roughly $70 a barrel before the war began in late February to above $119 at its peak. Energy analysts warned the blockade could push prices a further $5–$10 per barrel, with one expert noting it could remove an additional 2 million barrels per day from an already constrained market, compounding the roughly 10 million barrels per day already lost due to the conflict. Wheat, corn, and soybean futures also rose on fears over fertiliser supply disruptions. Share markets in South Korea and Australia fell sharply.

The blockade's legal standing is contested but not without precedent. Under the laws of naval warfare, a belligerent state — which the US unambiguously is in this conflict — can legally impose a blockade against another belligerent. However, critics note that the action almost certainly ends the ceasefire in legal terms and threatens to restart active hostilities. Australian Prime Minister Anthony Albanese said his government had not been asked to participate and called for the strait to remain "open for all" in accordance with international law. Whether the blockade holds, or whether economic and diplomatic pressure forces a rapid reversal, may become clear within days: one energy analyst suggested Trump could "walk it back by midweek" if oil prices continue to climb. For now, the Strait of Hormuz — the narrow chokepoint connecting the Persian Gulf to the wider world — sits at the centre of a crisis with no clear resolution in sight.