American forces have shot down a Syrian government fighter jet accused of attacking Kurdish-led troops, prompting a furious response from Damascus as tensions increase.

US Central Command said the SU-22 dropped bombs near the Syrian Democratic Forces (SDF), who are being supported by the US-led coalition as they advance on the terrorist stronghold of Raqqa.

“In accordance with rules of engagement and in collective self-defence of Coalition partnered forces, it was immediately shot down by a US F/A-18E Super Hornet,” a statement said.

“The Coalition's mission is to defeat Isis in Iraq and Syria. The Coalition does not seek to fight Syrian regime, Russian, or pro-regime forces partnered with them, but will not hesitate to defend Coalition or partner forces from any threat.

“The Coalition presence in Syria addresses the imminent threat Isis in Syria poses globally. The demonstrated hostile intent and actions of pro-regime forces toward Coalition and partner forces in Syria conducting legitimate counter-ISIS operations will not be tolerated.”

It was the most significant US attack on Bashar al-Assad's forces since April, when Donald Trump ordered missile strikes on a government airbase that launched a chemical attack.

Smoke rises from the al-Mishlab district at Raqqa’s southeastern outskirts on 7 June (Reuters)

American forces also attacked pro-government troops last month, then it bombed hostile units near an SDF training base in An Tanf.

Commanders from the anti-Isis mission codenamed Operation Inherent Resolve said the SDF-held town of Ja’din, near Tabqa on the outskirts of Raqqa, came under attack from pro-regime forces on Sunday afternoon.

The attack started at 4.30pm local time (2.30pm BST), wounding a number of SDF fighters and forcing them to flee the strategic town.

Planes from the US-led coalition “conducted a show of force” that stopped the initial advance by pro-Assad troops, a statement said, adding: “The Coalition [then ]contacted its Russian counterparts by telephone via an established 'de-confliction line' to de-escalate the situation and stop the firing.”

But at 6.43pm local time (4.30pm BST), the Syrian regime SU-22 dropped bombs near SDF fighters south of Tabqah and the US shot it down.

The account was contested by Syrian army commanders, who said the plane was bombing nearby Isis positions, rather than the SDF.

A statement carried by the state-owned Syrian Arab News Agency accused the US of “supporting terrorism” by attacking Assad's forces.

“The attack stresses coordination between the US and Isis, and it reveals the evil intentions of the US in administrating terrorism and investing it to pass the US-Zionist project in the region," the agency quoted general command as saying.

Syrian army 'crosses into Raqqa province'

Majd Fahd, a correspondent for website al-Masdar News, claimed the pilot was his cousin and a father-of-three. “You American bastards just shot down my cousin's aircraft (Ali) while taking out the scumbags of Isis in the area," he tweeted. “Your kids are waiting for you. Please come back safe and very soon.”

The outlet later reported clashes between the Syrian Arab Army and SDF in the area, after pro-regime troops reportedly attempted to cross the front line to recover the pilot.

American officials said Ja'din sits approximately a mile north of an established de-confliction zone between the SDF to the north and Syrian regime to the south.

“The Coalition calls on all parties to focus their efforts on the defeat of Isis, which is our common enemy and the greatest threat to regional and worldwide peace and security,” a spokesperson for US Central Command added.

The battle to drive Isis out of swathes of territory in northern Syria has brought opposing local and international actors into fresh conflict in the country’s six-year-long civil war.

The SDF, which incorporates the Kurdish People’s Protection Units (YPG), has been declared a terrorist group by Turkey and come under attack from rebels backed by Ankara, which perceives Kurdish gains along its border as a threat.

Assad’s forces have predominantly been fighting anti-government rebels and Islamist extremists including al-Qaeda linked groups, but are expected to increasingly turn their fire on the SDF as other targets wane.

Russia is supporting the Syrian government alongside Iran, while its rival Saudi Arabia is part of the US-led coalition bombing Isis.

British jets prepare for air strikes in Syria Show all 10 1 /10 British jets prepare for air strikes in Syria British jets prepare for air strikes in Syria A Tornado jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria Pilots and ground crew prepare combat aircraft Panavia Tornados at RAF Marham at RAF Marham, UK Getty British jets prepare for air strikes in Syria A Eurofighter Typhoon jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri British jets prepare for air strikes in Syria A Tornado jet ahead of taking off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria, the Ministry of Defence has confirmed. The air strikes were carried out within hours of a vote by MPs in the Commons to back extending operations against Isis from neighbouring Iraq British jets prepare for air strikes in Syria Personnel work on a British Tornado after it returned from a mission at RAF Akrotiri in southern Cyprus British jets prepare for air strikes in Syria Two RAF Tornado GR4's, both with remaining weapons ordnance, approach RAF Akrotiri in Cyprus, as they return to the base after carrying out some of the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado takes off from RAF Akrotiri, on the Mediterranean island nation of Cyprus British jets prepare for air strikes in Syria A Tornado jet leaving RAF Lossiemouth in Scotland British jets prepare for air strikes in Syria AKA RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri, Cyprus. The RAF has sent two further Tornado aircraft and six Typhoons to bolster aircraft now flying sorties to both Iraq and Syria

The coalition is supporting the SDF’s advance on Isis’ de-facto capital of Raqqa with air strikes, while members have also given training and support to selected anti-Isis groups, and American and British special forces are on the ground.

The UN warned this week that the bombing campaign is killing a “staggering” number of civilians in Isis-held territory, with air strikes continuing to intensify.

Iran's Revolutionary Guard said it launched its own air strikes against Isis on Sunday, in response to terror attacks on the parliament building and a shrine on Tehran.

Tehran said surface-to-surface medium range missiles hit Deir Ezzor province, where militants fleeing the advance on Raqqa are fortifying their positions.

A statement said they were launched from Iran's Kurdistan and Kermanshah provinces, where footage shared on social media appeared to show the missiles rise in an orange glow before heading over Iraq towards their targets.

The Revolutionary Guard said many “terrorists” were killed and their weapons had been destroyed in the strike but the account could not be independently confirmed.

A statement warned Isis militants and their “regional and international supporters” of further attacks in retaliation to any future atrocities in Iran.