Donald Trump said Iran cannot 'blackmail' the US after the Middle Eastern country threatened to close the Strait of Hormuz again. 

The President addressed the deepening crisis during a Q&A session on Saturday, shortly after he signed an unrelated executive order to ease access to a psychedelic drug used to treat PTSD.

Trump revealed that talks between the US and Iran are 'going very well,' despite the issue with Iran opening and closing the Strait and threatening ships that enter the oil-rich area. 

'They wanted to close up the Strait again, as they've been doing for years, but they can't blackmail us,' Trump said. 

'We'll have some information by the end of the day,' he continued. 'We're talking to them. We're taking a tough stand. They've killed a lot of people. A lot of our people have been killed.' 

It comes amid reports Iran opened fire on Saturday on ships trying to cross the Strait of Hormuz after shutting the key waterway again.

At least two Indian merchant vessels reported being hit by gunfire as they attempted to pass through the narrow waterway, three shipping and security sources told Reuters.

The extent of the damage was not immediately clear. One of the vessels was carrying 2 million barrels of Iraqi oil.

Iran's new Supreme Leader, Mojtaba Khamenei, said Iran's navy was ready to inflict 'new bitter defeats' on its enemies in a message posted on Telegram.

The convoy that had begun moving through the strait quickly scattered, with vessel tracking data showing ships dispersing after what had been the first major movement since the start of the war.

It came after Iran moved to re-start the blockade, saying the Strait of Hormuz had been shut once more after the US refused to lift what Tehran describes as a naval blockade of its ports.

Trump warned he could 'start dropping bombs again' if the fragile ceasefire collapses.

The President insisted a US naval blockade of Iranian ports would remain in place until a deal is reached, prompting fresh warnings from Tehran it could shut the route again.

Trump said on Saturday he is still weighing whether to extend the truce, warning military action remains on the table if talks fail.

He discussed the latest with Iran at a press conference where he signed an executive order to speed up the process of using psychedelic drugs to treat veterans' PTSD.  

The President brought out advocate Joe Rogan to make the announcement who he said emailed him about the treatment, sparking his interest.

'Today, we're bringing them new hope,' he said, as Rogan and RFK Jr stood behind him in the Oval Office. 

'I think you're going to see a big difference and a big reduction in that number [of suicides].' 

The drug being studied is ibogaine, Trump said, as he announced a $50million investment for research and help speed up the process to get it FDA approved. 

Ibogaine is a naturally occurring psychoactive from the root of a shrub native to Central Africa. 

It has gained popularity in recent years and generated the attention of medical professionals and of Rogan.

Trump said the study found an 80 to 90 percent reduction in symptoms of depression and anxiety within one month of use. 

A study found that when combined with magnesium to protect the heart, the drug safely and effectively reduced PTSD, anxiety and depression.

'Can I have some, please?' the President joked, to a roar of laughter. 'I'll take whatever it takes!'

He later backtracked, saying: 'I don't have time to be depressed. You know, if you stay busy enough, maybe that works too. That's what I do.'

Robert F Kennedy Jr, the health secretary, said the executive order comes amid concerns veterans were desperately traveling to Mexico and other countries to get the drug for relief, as it was not available in the US.

Rogan also spoke at the event, saying he sent the President an email about ibogaine, to which Trump reportedly replied: 'Sounds great! Do you want FDA approval? Let's do it.'

'It was literally that quick,' Rogan said, before thanking Trump for his work in speeding up the process.