Oil prices jumped and share markets fell after Donald Trump said the US would again block Iranian shipping in the Strait of Hormuz and impose a 20% toll on other eligible cargo using the route. The move followed further US strikes on Iran and retaliatory action from Tehran, deepening uncertainty over one of the world’s most important energy chokepoints. It matters because disruption in Hormuz threatens global oil and gas supplies, raising energy costs and unsettling wider financial markets.

Brent crude rose 5% to $79.37 a barrel, having traded at $72.48 before US-Israeli strikes on Tehran in late February and reaching as high as $120 in April. US stocks weakened, with the Nasdaq down 1% and the S&P 500 0.4%, while Asian markets fell more sharply: South Korea’s Kospi dropped 8%, and Japan’s Nikkei 225 and China’s Shanghai Composite each lost 2%; chipmakers SK Hynix and Samsung fell 15% and 10% respectively. About a fifth of the world’s oil normally passes through Hormuz, but shipping is already slowing, with data firm Kpler reporting just six vessels crossed on Sunday, the lowest number in five weeks.