"Strike our assets and you get struck," Iranian Parliament Speaker Mohammad Bagher Ghalibaf said after US and Iranian strikes on shipping at the weekend that pushed oil prices up to near six-week highs on Monday.
The latest threat underscores the risks of further escalation, with no sign of progress towards a diplomatic breakthrough that could end more than six months of conflict and restore normal energy flows through the Gulf.
Iran has tightened restrictions on shipping through the Strait of Hormuz, a critical artery for global oil and gas supplies, since the war began with US and Israeli strikes on February 28.
On Sunday, senior Iranian security official Mohsen Rezaei said Tehran would soon announce a new restricted zone in the Gulf and unveil a shipping corridor through the strait.
Rezaei said the zone would begin where a US naval blockade of Iran starts and extend into parts of the Gulf. Any vessel entering the area would be placed on an Iranian sanctions list.
"We will only commit to the Strait of Hormuz being open when (the Americans) stop the sabotage, threats and attacks on Iran," Rezaei said.
Ghalibaf later reinforced Tehran's warning in what appeared to be a response to US Defense Secretary Pete Hegseth, who had described Iran's oil tanker fleet as "defenceless".
"It's simple: the oil and gas production chain here is sprawling, accessible, and exposed. American oil and gas companies across these waters and facilities share that exposure," Ghalibaf, who is Iran's top negotiator, wrote on social media.
Regional tensions were heightened by Israeli strikes on a town in southern Lebanon that killed at least 12 people on Monday, according to Lebanon's health ministry, marking one of the deadliest days of bombardment in recent weeks.
The attacks have fuelled fears of a renewed Israeli military campaign despite a June ceasefire with the Iran-backed Hezbollah group.
They also complicate efforts to end the wider conflict, with Tehran insisting that any lasting agreement with Washington must include an end to Israeli attacks in Lebanon.
After a relative lull through much of August, hostilities have intensified again following the collapse of an interim ceasefire reached in June. Diplomatic efforts have made little headway.
On Saturday, US forces struck three Iranian oil tankers, including one near Kharg Island, Iran's main oil export hub, according to US Central Command.
The attacks followed strikes by Iran's Revolutionary Guards on US warships operating in the region.
Tehran has demonstrated it can still attack US interests in neighbouring countries and disrupt oil flows through the Strait of Hormuz.
Shipping data showed an average of just 10 commodity vessels per day transited the strait over the past 10 days, the lowest level since May.
Iran has said it will step up efforts to tackle problems created by US sanctions that are crippling its economy.
Ghalibaf acknowledged at the weekend that Iran's struggle was no longer confined to the battlefield. Alongside the military confrontation, he said, the country faced major domestic challenges including inflation, unemployment, currency volatility and market instability.
The conflict has also impacted oil-producing Gulf Arab states such as the United Arab Emirates, which has come under fire from Iranian missiles and suffered attacks on its oil tankers in the Strait of Hormuz.
UAE presidential adviser Anwar Gargash said on Monday the country was building alternative routes for its energy exports and trade to ensure they are not "held hostage" by the war.
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