Iran has called on Syria to 'make Americans regret their attack' after Russia warned Donald Trump there will be a military response if the US strikes at Assad again.

President Hassan Rouhani accused the US of not acting 'within international frameworks' before condemning America's surprise bombardment of a Syrian airbase.

It comes after both Russian and Iranian forces warned Trump they would retaliate with military action if the US President launched more strikes against Bashar al-Assad's forces.

Rouhani said: 'Americans have never acted within international frameworks, and one instance is the sanctions they impose against Iran, unreasonably considering themselves as the world's leader.

'The Syrian people and army must give a response (to the US) that makes Americans regret their attack.'

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Iranian President Hassan Rouhani (pictured today) has accused the US of not acting 'within international frameworks' before condemning America's surprise bombardment on a Syrian airbase

Russian and Iranian forces warned Donald Trump (pictured arriving at the White House on Sunday) they would retaliate with military action if he launched more airstrikes on Syria

Russian President Vladimir Putin met with President of the Islamic Republic of Iran Hassan Rouhani in Moscow on March 28

The fallout comes after President Trump ordered airstrikes (pictured) on a Syrian airbase in the first direct attack by the US against Assad

Rouhani called his critics 'smoke machines, disseminating black smoke everywhere' and also criticised the United States for imposing sanctions on Iran.

Last night, in an ominous threat raising the prospect of war, Iranian and Russian forces said the US President had crossed a 'red line' with his missile attack.

'From now on we will respond with force to any breach of red lines and America knows our ability to respond well,' the military chiefs said in a joint statement with militant group Hezbollah.

The Russian Embassy in London suggested on Sunday night there could be 'real war' if Moscow is presented with an ultimatum over Syria.

But UK Foreign Secretary Boris Johnson will lead a push on Monday for Russia to face tough new sanctions unless it withdraws its support for Assad.

At a G7 meeting in Italy, Johnson will call for Moscow to be threatened with isolation from the international community and a raft of economic punishments.

Johnson also insisted the US could carry out further strikes against the Syrian regime over use of chemical weapons.

Russia was kicked out of the club of industrialized nations, formerly the G-8, after its 2014 annexation of Ukraine's Crimea region and assistance for pro-Russian separatists in eastern Ukraine.

But the prospect of being allowed back into the elite club is also expected to be held out as an incentive for cooperating.

Secretary of State Rex Tillerson has said the US will stand up to anyone who commits crimes against humanity.

EU High Representative for Foreign Affairs Federica Mogherini (L), US Secretary of State Rex Tillerson (C) and Italy's Foreign Minister Angelino Alfano arrive to attend a ceremony at the Sant'Anna di Stazzema memorial - Tillerson said the US will stand up to anyone who commits crimes against humanity

Speaking today, ahead of a Group of 7 meeting in Italy, Tillerson said: 'We rededicate ourselves to holding to account any and all who commit crimes against the innocents anywhere in the world.'

During a visit to a site of Nazi atrocities in Italy during World War II, Tillerson said Sant'Anna di Stazzema 'will serve as an inspiration to us all.' The Nazis killed more than 500 civilians in the village in 1944.

As tensions escalated:

The Kremlin mocked Britain for having 'no real influence on the course of international affairs' after Mr Johnson cancelled a planned trip to Moscow;

UK's Defence Secretary Sir Michael Fallon said Russia was responsible for 'every civilian death' in Assad's chemical weapons attack on his own people;

America warned Moscow it faces a 'relationship of competition and potential conflict' unless it stops supporting Assad's 'murderous regime';

The White House told North Korea it should take US missile strikes against Syria as a warning that America is prepared to take military action against countries which break international agreements.

Despite the looming threat of war following the decision to launch airstrikes, Trump made his way on to his golf course in West Palm Beach, Florida on Sunday - marking his 16th visit to one of his own courses since he became president.

During the election campaign, Trump said that as president he would probably never see his own golf courses again because he'd be too busy working.

He also repeatedly attacked Barack Obama's golf trips and vacations for at least five years during the previous administration and begged the former president not to attack Syria back in 2013.

Rouhani (pictured) has called on Syria to 'make Americans regret their attack' after Russia warned Donald Trump there will be a military response if the US strikes at Assad again

Trump gave a thumb's up after arriving on theSouth Lawn last night onboard Marine One

Trump managed to play some golf on one of his own courses before returning to Washington

Trump, pictured, authorized the strikes on the Syrian airfield while at his Mar-a-Lago estate

President Trump called to congratulate the commanding officers on the Syrian missile strike from aboard Air Force One (above) with National Security Advisor H.R. McMaster

The commanding officers of Arleigh Burke-class guided-missile destroyers USS Ross and USS Porter received phone calls from Trump following the Syrian missile strike

But in the early hours of Friday morning, President Trump himself ordered airstrikes on a Syrian airbase in the first direct attack by the US against Assad.

The onslaught of 59 cruise missiles followed a suspected chemical attack on the rebel-held town of Khan Sheikhun in northern Syria which killed 87 civilians, including many children.

A joint command centre of Russia, Iran and Islamist militant group Hezbollah warned America they would not allow further attacks on the Syrian regime.

In a statement they said: 'What America waged in an aggression on Syria is a crossing of red lines. From now on we will respond with force to any aggressor or any breach of red lines from whoever it is and America knows our ability to respond well.'

The phrasing appeared to be a mocking reference to Barack Obama's warning in 2012 that Assad should not cross a 'red line' by using chemical weapons.

President Donald Trump visited one of his own golf courses in West Palm Beach, Florida on Sunday for the 16th time in his brief presidency

Trump (pictured Sunday leaving Mar-a-Lago) is far outpacing his predecessor Barack Obama, who he repeatedly criticized for playing golf while he was president

In 2013, Trump urged Obama not to attack Syria, before criticizing him for playing golf

In a further sign of increasing tensions, the Russian Embassy in London responded with anger to claims the G7 – Canada, France, Germany, Italy, Japan, Britain and America – could today agree to slap Putin with the threat of sanctions unless he pulls his troops out of Syria and ends his support for Assad.

In a series of provocative tweets on its official account, the embassy suggested that if Russia were given an ultimatum, the outcome would be either, 'war of clowns, war of muses, a conventional war or a mix of the above'.

The Russian Embassy in London responded with anger to claims the G7 could agree to slap Putin (shown) with the threat of sanctions

It added: 'If G7 ultimatum to Russia brings us to real war, what is your trust in @realDonaldTrump as a wartime leader & @BorisJohnson as his lieutenant?' Iran's supreme leader, Ayatollah Ali Khamenei, last night said the US had made a 'strategic mistake' by attacking Syria.

He made clear he was not intimidated by claims the airstrike was a warning that America was willing to target other countries. Tehran has been a key backer of Assad in Syria's six-year civil war.

'The Islamic Republic of Iran will not leave the field in the face of threats. Former American officials created Daesh [Islamic State] and the current leaders are reinforcing it,' Khamenei said.

Trump administration officials yesterday blamed Russian inaction for enabling the deadly poison gas attack against Syrian civilians last week. US Secretary of State Rex Tillerson said Syria was able to execute the attack, which killed scores of people, because Moscow had failed to carry out a 2013 agreement to secure and destroy chemical weapons in the country.

White House national security adviser HR McMaster said Syria's 'sponsors', Russia and Iran, were enabling Assad's 'campaign of mass murder against his own civilians'.

In an ominous threat raising the prospect of war, Russia and Iran said the US President had crossed a 'red line' with his bombardment on the forces of Bashar al-Assad (shown)

Crew members at the launching of the Kazan, a Project 885M Yasen-class nuclear-powered multipurpose attack submarine, at the Sevmash shipyard

He said the US would take further action in Syria if necessary. 'We're prepared to do more. The president will make whatever decision he thinks is in the best interests of the American people,' he told Fox News.

Mr McMaster said Moscow was supporting 'a murderous regime' and its actions would dictate the future of US-Russian relations.

'Do they want it to be a relationship of competition and potential conflict,' he said. 'Or do they want it to be a relationship in which we can find areas of co-operation that are in our mutual interest?'

Last night a US strike group led by an aircraft carrier steamed toward the Korean peninsula as US Secretary of State Rex Tillerson said the strikes against Syria carried a message for any nation operating outside of international norms.

'If you violate international agreements … if you become a threat to others, at some point a response is likely to be undertaken,' he told ABC TV.

Mr McMaster said it was 'prudent' to send the strike group, criticising North Korea as a rogue, nuclear-armed nation engaged in provocative behaviour.