The Strait of Hormuz has been closed to shipping following an Iranian attack on a US naval base in Bahrain, marking a severe escalation in regional tensions and a direct threat to global energy flows.
Iran announced the strikes on Saturday in response to recent US air operations along its southern coast, accusing Washington of violating a ceasefire agreement intended to end a four-month conflict.
Vance responded by insisting the US has adhered to the deal, warning that "violence will be met with violence."
The closure of the strait, through which roughly a fifth of the world's oil passes, immediately raises the risk of significant supply disruptions.
Markets are likely to react to the heightened geopolitical premium, with Brent crude and shipping freight rates facing upward pressure as traders price in the potential for prolonged transit delays.
The incident follows a recent attack on a tanker in the same corridor, which had already reignited concerns about shipping security in the region.
This development represents a sharp deterioration in the security environment for maritime trade.