DUBAI/CAIRO - The United States struck bridges in Iran, and Tehran responded by hitting a power and desalination plant in Kuwait on July 17, as the two sides risked further escalation by expanding their targets to include infrastructure.

At sea, where the renewed conflict has again cut off energy supplies from the Gulf, US Marines boarded a tanker near the Strait of Hormuz.

Armed men seized another vessel off Yemen, raising concern over security in the Middle East’s other big choke point for oil shipments at the mouth of the Red Sea.

Iran’s semi-official Tasnim news agency reported late on July 17 that the Revolutionary Guards navy had “targeted” a Thai-flagged ship trying to get through the Strait of Hormuz.

It did not give further details.

Washington and Tehran have been testing the limits of escalation since their ceasefire agreement collapsed last week, raising the prospect of a return to all-out war.

After reports of the escalation on July 17, benchmark Brent crude oil prices climbed 3 per cent and were on track for a third consecutive weekly gain, putting political pressure on US President Donald Trump ahead of November congressional elections.

Trump has threatened to launch broad-based air strikes on Iran’s infrastructure and has also declined to rule out a ground assault on Iran’s coast or islands.

US officials have said attacks on southern Iran are designed in part to give Trump options. Such moves risk provoking Iran to escalate in turn by hitting the vital infrastructure of vulnerable Gulf states, or having its allies in Yemen further disrupt global energy supplies by attacking shipping from the Red Sea.

Mohsen Rezaei, an adviser to Iran’s supreme leader, warned on July 17 against US escalation or any attempt to seize Iranian territory.

“If US strikes continue for several more days, we will move into a phase of full-scale offensive operations,” Rezaei, a former Revolutionar...