Donald Trump’s horror run of international diplomacy continues with Iran warning the US faces “the mother of all wars” if it pursues tough new sanctions against the Middle East power.

Tehran faces increased US pressure and looming sanctions after Mr Trump’s decision to withdraw the United States from a 2015 international deal over Iran’s nuclear program.

Iranian President Hassan Rouhani on Monday morning (AEST) cautioned Mr Trump about continuing to pursue hostile policies against Tehran.

“Mr Trump, don’t play with the lion’s tail, this would only lead to regret. America should know that peace with Iran is the mother of all peace, and war with Iran is the mother of all wars,” Mr Rouhani told a gathering of diplomats, leaving open the possibility of peace between the two countries, at odds since the 1979 Islamic Revolution.

“You are not in a position to incite the Iranian nation against Iran’s security and interests,” he added, in an apparent reference to reported efforts by Washington to destabilise Iran’s Islamic government.

Mr Trump is still working to regain the support of his Republican party after being widely criticised for his perceived soft approach to Russian President Vladimir Putin at their summit in Helsinki last week.

That meeting culminated a fractious European trip that saw him criticise Germany over its reliance on Russia, demand America’s NATO allies spend more on defence and ridicule British Prime Minister Theresa May’s Brexit deal,

In Washington, US officials familiar with the matter said that the Trump administration had launched an offensive of speeches and online communications meant to foment unrest and help pressure Iran to end its nuclear programme and its support of militant groups.

Current and former US officials said the campaign painted Iranian leaders in a harsh light, at times using information that is exaggerated or contradicts other official pronouncements, including comments by previous administrations.

Mr Rouhani scoffed at Mr Trump’s threat to halt Iranian oil exports and said Iran has a dominant position in the Gulf and the Strait of Hormuz, a major oil shipping waterway.

“Anyone who understands the rudiments of politics doesn’t say ‘we will stop Iran’s oil exports’ … we have been the guarantor of the regional waterway’s security throughout history,” Rouhani said, cited by the semi-official ISNA news agency.

Iran’s Supreme Leader Ayatollah Ali Khamenei on Saturday backed Rouhani’s suggestion that Iran may block Gulf oil exports if its own exports are halted.

Mr Trump declared the Iran nuclear deal “rotten to the core” when deciding to pull out in May.

“It is clear to me that we cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement,” he said at the time.

“The Iran deal is defective at its core. If we do nothing we know exactly what will happen.”

US Secretary of State Mike Pompeo later vowed the US would “crush” Iran’s influence in the Middle East by imposing the “strongest sanctions in history”.

“The leaders in Tehran will have no doubt about our seriousness,” Mr Pompeo warned in a May 22 speech. 

“These will end up being the strongest sanctions in history by the time we are complete,” he told Washington-based conservative think tank, the Heritage Foundation.

Iranian officials have in the past threatened to block the Strait of Hormuz in retaliation for any hostile US action.

-with AAP