Following the breakdown of diplomatic negotiations in Islamabad led by Vice-President JD Vance, President Donald Trump announced a naval blockade of Iran on Sunday morning via a series of Truth Social posts. Trump declared that the US would impose a naval blockade, stating, "No one who pays an illegal toll will have safe passage on the high seas." He also affirmed that the US would continue mine-clearing operations in the Strait of Hormuz to ensure safe passage for allied shipping, adding that the military was "locked and loaded" and prepared for further attacks. While Trump suggested progress was made in the 20-hour talks, he stated Iran refused to abandon its nuclear ambitions. However, a US official familiar with the negotiations contradicted this, citing a broader range of disagreements including Iran's control of Hormuz and its support for regional proxies such as Houthi rebels and Hezbollah.

The US military Central Command (CENTCOM) later clarified the blockade's scope, announcing it would stop all ships traveling to or from Iranian ports, a condition different from Trump's initial proposal. This blockade, enforced impartially against vessels of all nations entering or departing Iranian ports and coastal areas, began at 10 AM ET on Monday. CENTCOM also specified that US forces would not impede vessels transiting to or from non-Iranian ports in the Strait of Hormuz. Senator Mark Warner, a Democrat on the Senate Intelligence Committee, questioned the blockade's effectiveness, while Republican congressman Mike Turner supported it as a means to force a resolution. Iran, through its state IRIB news agency, asserted its continued control over the Strait of Hormuz, stating that enemy-affiliated vessels do not have the right to pass through its territorial waters and warned that if Iranian ports are targeted, "no port in the Persian Gulf and the Sea of Oman will be safe." The Islamic Revolutionary Guard Corps (IRGC) Naval Forces further threatened severe action against military vessels approaching the strait.

The UK government swiftly distanced itself from enforcing the US blockade, with a spokesperson stating that British naval ships and soldiers would not be used to block Iranian ports. UK minesweepers and anti-drone capabilities will continue operating in the region. Prime Minister Sir Keir Starmer urged "de-escalation" and called for a wide coalition to protect freedom of navigation in the Strait of Hormuz, emphasizing that ships should not be subject to tolls, following reports of Iran demanding $2 million in transit fees. Singapore's Foreign Minister Vivian Balakrishnan echoed this sentiment, firmly stating that Iran has no right to demand negotiations or tolls for safe passage, upholding the principle of freedom of navigation under international law.

The Strait of Hormuz, a critical chokepoint through which roughly a fifth of global oil supply flows, has become a major flashpoint. Iran's previous actions, including reckless mining of the waterway, had already caused daily shipping traffic to plummet from 138 vessels to single digits. The failure of negotiations and the announcement of the blockade immediately sent global oil prices surging. Brent crude rose by 8.5% to $102.37, while West Texas Intermediate was up 9% at $105.34. The market is pricing in not just lost barrels but significant uncertainty. This geopolitical event is rapidly becoming a macroeconomic shock, with rising oil prices feeding into broader inflation through increased fuel, electricity, logistics, food, and manufacturing costs. This process has already begun, with headline inflation ticking up in the United States and forward inflation expectations rising in Europe.

Central banks face a difficult challenge as this is a supply-side shock, not demand-led inflation. Raising interest rates will not increase oil supply or reopen shipping lanes. However, failing to act risks allowing inflation expectations to drift, an outcome that proved costly during historical oil crises like 1973 and 1979, which led to stagflation. Modern economies, still recovering from recent inflation cycles and burdened by high debt, have less policy space. Financial markets are adjusting, with bond yields reflecting renewed inflation risk and equity markets showing volatility. Emerging markets are particularly vulnerable, facing imported inflation and pressure on foreign exchange markets.

Fitch Ratings notes that a prolonged Iran war leading to sustained high oil prices would have mixed impacts on African banking sectors, largely dependent on sovereign ratings. Such a scenario would renew inflationary pressures in net hydrocarbon importers like South Africa, Kenya, Morocco, and Tunisia, and could lead to fuel shortages and currency pressures. While African central banks might tighten monetary policy, weighing on economic growth, African banks generally possess strong operating profits and capital buffers to accommodate these challenges. The current conflict highlights the global economy's deep reliance on stable and affordable energy flows, a vulnerability exposed despite ongoing energy transition efforts. This situation underscores that price stability depends not only on monetary discipline but also on the stability of the physical systems underpinning the economy.