US-backed forces in Iraq and in Syria are in the process of rooting Islamic State (IS) fighters out of their strongholds in northern Iraq and eastern Syria.

In the case of Mosul in Iraq, the removal of diehard IS remnants might be completed any day now. In Raqqa, the IS headquarters in eastern Syria, US-backed rebel forces are in the town’s suburbs.

How long it will take for Syrian Democratic Forces (SDF), made up of Arab and Kurdish militias supported by US artillery and airstrikes, to rid Raqqa of IS and at what cost is anyone’s guess. But it seems clear we are entering the final battle for what has served as the so-called caliphate’s headquarters.

However, what should be understood is the Syrian conflict is far from any sort of long-term resolution. It may be on the verge of becoming more complex and thus more dangerous.

The world is now observing a potentially highly volatile stage in the post-IS fight for Syria, with interested parties manoeuvring for what might be described as the “next game” – certainly not the “endgame”. Latest developments are bringing the US and its allies in Syria into closer proximity to – and possible direct conflict with – the Iranian-backed Bashar al-Assad regime, and Iran itself.

Iran’s Islamic Revolutionary Guards Corps commanders and Lebanese Hezbollah and Iraqi Shiite militias are on the ground in Syria fighting alongside Assad forces to regain territory and re-establish Damascus’s sovereignty over the entire country.

This is a fight to the death.

From Iran’s perspective, Syria – ruled by a heterodox Shiite sect – represents a vital piece in its Middle East designs. This is not least because it provides a corridor to its Hezbollah Shiite co-religionists in Lebanon. This is why it continues to invest heavily in propping up the Assad regime. A Syrian setback would be crippling for its regional ambitions.

Risks of the US and Iran rubbing up against each other in Syria and precipitating a wider conflagration are incalculable in circumstances in which America’s Middle East policy is in flux, if not in chaos. Not helping is the impression that elements of the Trump administration are spoiling for a fight with Iran without comprehending wider consequences.

And then there’s Russia. It may not have forces on the ground, but its warplanes in Assad’s service are part of a toxic brew that threatens a wider Middle East conflict. Risks grow by the day.

What is clear – as Iraqi forces retake a shattered Mosul and Syrian anti-Assad regime rebels push further into Raqqa – is that contesting forces in Syria are battling over the country’s shattered post-IS corpse. Where this will end is impossible to predict, but as a rule of thumb in the Middle East these sorts of situations do not end well.

Tensions – and risks – were underscored earlier this month when the US shot down a Syrian Russian-supplied jet in airspace to the south of Raqqa. The US has also brought down several Iranian drones in hotly costed territory around the Euphrates.

What is transpiring as an IS “caliphate” shrinks east towards the Iraq border from Raqqa is the emergence of a vacuum that various players are striving to fill, including principally the Assad regime, having regained control of the west of Syria.

Where this will go next is not clear, not least because the US has not indicated the extent to which it plans to continue to involve itself on the ground beyond rooting out IS from its Raqqa redoubt. Will it step aside when and if Raqqa falls, enabling Syrian government forces, backed by Iran and Russia and with the participation of Lebanese and Iraqi militias, to regain control of lost territory? Or will it remain a factor?

Journalist Jonathan Spyer, who has spent years reporting on the Syrian conflict and its implications for the wider Middle East, is at a loss to interpret US policy in Syria beyond its confrontation with IS. As he writes in Foreign Policy:

The crucial missing factor here is a clearly stated US policy. Trump can either acquiesce to the new realities that Russia seeks to impose in the air, and that Iran seeks to impose on the ground, or he can move to defy and reverse these, opening up the risk of a potential confrontation. There isn’t really a third choice.

Spyer quotes the Iranian Fars News Agency as saying ominously:

The imbroglio in eastern Syria has only begun. Stormy days are ahead of us.

That might be regarded as an understatement. What is clear is that the US cannot expand its presence in eastern Syria without engaging the Iranian-backed Syrian regime. As Faysal Itani of the Atlantic Council’s Rafik Hariri Centre for the Middle East observes:

The United States cannot tiptoe around Iran and the Syrian regime while capturing strategic territory and resources.

While Russia does not seek a confrontation, it appears unable (or unwilling) to restrain its allies. The United States does not seem to have decided whether fighting IS only to empower Iran and Assad would be worthwhile, or whether there is a feasible way, at an acceptable cost, to beat the Islamic State without strengthening US adversaries … It’s perfectly clear now that choosing which wars to fight or ignore in Syria is not possible – and it probably never was.

From an Australian perspective, Syria presents a concerning spectacle. Canberra suspended missions by the Royal Australian Airforce over Syria (not Iraq) after the US shooting down of the Syrian warplane out of concern over a suspension of “deconfliction” arrangements with Russia. It is not clear whether those missions have resumed.

More broadly, deeper US involvement in the Syrian conflict would potentially pose challenges for an Australian government – if indeed a request was made for on-the-ground assistance.

At this stage there is no sign of that occurring. But Australia should be prepared for an unravelling of circumstances in Syria and be ready for any eventualities. Needless to say, it should hasten slowly.

In all of this, it doesn’t take much imagination to consider what would be nightmare scenario in which the US and Iran found themselves at war. As Nader Hashem, director of the Centre for Middle Eastern Studies at the University of Denver and an expert of sectarian conflict in the region, has observed:

I suspect the biggest problem is a clash between American and Iranian forces somewhere in Syria where there will be a major loss of life, and then a slow, steady decline toward war with Iran, where Iran chooses to retaliate in the Persian Gulf with American shipping or some sort of escalation along those lines. That would have huge consequences for the nuclear agreement and the broader stabilisation of the region.

Indeed.