US President Donald Trump has discussed how to mitigate the effects of a possible months-long US blockade of Iran's ports with US oil companies, a White House official says, as the president urged Iran to "get smart soon" and sign a deal.
Tuesday's talks with oil executives followed deadlock in efforts to resolve the conflict, which has led the United States to try to squeeze Iran's oil exports with a naval blockade to try to force it to reopen the Strait of Hormuz to shipping.
Trump has said Iran can call if it wants to talk and, in a post on Truth Social on Wednesday before details of the meeting emerged, said Iran "couldn't get its act together".
Trump said on Wednesday Iran talks were being conducted by phone after he cancelled a trip over the weekend for US negotiators to travel to Pakistan to speak with Iranian officials.
Trump and the oil executives on Wednesday "discussed the steps President Trump has taken to alleviate global oil markets and steps we could take to continue the current blockade for months if needed and minimise impact on American consumers," the White House official said.
Oil prices rose more than six per cent on Wednesday, with the Brent contract hitting a one-month high, on the prospect of a lengthy blockade.
The war has cost the United States $US25 billion ($A35 billion) so far, a senior Pentagon official said on Wednesday, providing the first official estimate of the military's price tag for the conflict.
Iran has pledged to continue disrupting traffic through the strait as long as it is threatened, which may mean more Middle East oil supply disruptions from the conflict which has killed thousands and caused global economic upheaval.
Iranian authorities warned on Wednesday of "unprecedented military action" against continued US blockading of Iran-linked vessels.
Trump has said Iran cannot have a nuclear weapon while Iran says its nuclear ambitions are peaceful.
"They don't know how to sign a non-nuclear deal. They'd better get smart soon!" Trump said in the social media post, without explaining what such a deal would entail.
It featured a mock-up image of him in dark glasses and wielding a machinegun with the caption "No more Mr Nice Guy".
Iran wants US acknowledgement of its right to enrich uranium for what it says are peaceful civilian purposes.
It has a stockpile of about 440kg of uranium enriched to 60 per cent, material that could be used for several nuclear weapons if further enriched.
Iran's parliament Speaker and top negotiator Mohammad Baqer Qalibaf said Trump was trying to divide Iranians and force Iran to surrender through the blockade.
"The solution for confronting the enemy's new conspiracy is only one thing: maintaining unity, which has been the bane of all the enemy's conspiracies," Qalibaf said in an audio message on Telegram.
In a sign of the economic toll the war is taking on Iran's economy, its currency fell to a record low of 1,810,000 rials to the US dollar on Wednesday, the Iranian Students' News Agency said, as demand for foreign currency that built up during six weeks of fighting was now flowing into the open market.
The rial's value has fallen nearly 15 per cent in the last two days alone, ISNA reported.
Inflation for the month from March 20 to April 20 was 65.8 per cent, the central bank said, a trend likely to be exacerbated by the currency's plunge.
