An Iraqi PMF medic takes an Isis sign down and places a Shia militia (PMF) in it's place in the town of Ba'aj near the Iraq-Syria border. The Popular Mobilisation Front (PMF) forces are composed of majority shiite militia and are part of the Iraqi state forces. They have pushed Isis militants from an Iraq border strip back into Syria.

ANALYSIS: Could we be sleepwalking towards another major war in the Middle East?

On Sunday, an American jet downed a regime fighter aircraft, provoking a Russian threat to target the United States and its allies flying over eastern Syria.

Such "incidents" are piling up as world, regional and local powers race for turf and influence ahead of the mooted collapse of Islamic State (Isis) in Syria.

AL JAZEERA Iranian Revolutionary Guard has targeted bases of Isis in Syria's Deir Az Zor in retaliation for the June 7 attacks in Tehran.

Washington says its F-18 Super Hornet retaliated after the Syrian Su-22 fighter-bomber dropped its payload near Tabqa, an area close to the Syria-Iraq border occupied by the Syrian Democratic Forces (SDF), a US-backed militia in the fight against Isis.

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Denouncing the US strike as a "flagrant violation of international law", Moscow suspended its "deconfliction" hotline with the US military, which is intended to minimise "incidents" in Syrian skies, crowded as they are with US, Russian, Syrian, Turkish, Israeli and Australian aircraft.

RODI SAID/REUTERS A fighter from Syrian Democratic Forces (SDF), a US-backed militia in the fight against Isis sits in his vehicle in Raqqa province,Syria.

A statement by the Russian Defence Ministry was blunt: "All flying objects, including planes and drones of the international [US-led] coalition, detected west of the Euphrates [River], will be followed by Russian air defence systems as targets."

We've been here before. In April, Moscow was equally indignant and protested by temporarily suspending the deconfliction hotline after US President Donald Trump authorised a Tomahawk missile attack on a Syrian airbase from which the regime had launched a chemical weapons strike on its own civilians.

But while the latest attack by the US and its April prequel grabbed headlines, a series of recent, lower-profile "incidents", all in Syria's south-east, are prompting analysts to warn that Washington needs to tread more carefully - unless it wants to find itself on a collision course with Iran.

REUTERS TV The leader of the Isis group, Abu Bakr al-Baghdadi, delivering a sermon at a mosque in Mosul in July 2014. Russia's military says it may have killed him.

While the Americans were taking out the Syrian jet on Sunday, Iran fired a missile barrage into eastern Syria – the target for which it said was Isis, in retaliation for twin terror attacks in Tehran on June 7 claimed by the militant group.

Trump is escalating his anti-Iran rhetoric, and testifying before the Senate last week, US Secretary of State Rex Tillerson said that Washington would "work toward support of those elements inside of Iran that would lead to a peaceful transition".

That kind of talk in Washington and events in Syria prompted Iran scholar Trita Parsi to describe the situation as "explosive".

TIMA AGENCY A man holds a picture of the founder of the Islamic Republic Ayatollah Ruhollah Khomeini during a ceremony marking his death anniversary, in Tehran, Iran, earlier this month.

"An impression is given that this is an accidental escalation, but I'm not sure," he said. "Look at the totality of the Trump administration's statements on Iran – sanctions, hints of regime change, no diplomacy … these were the ingredients of the Iraq war."

The US and Iran have been able to tolerate each other in the Iraqi theatre. But their arm's-length coexistence in Iraq is likely to crumble once the Isis strongholds of Raqqa and Mosul fall, leaving a power vacuum in the border region.

Propped up by Moscow's power in the air and Tehran's Shiite militias on the ground, Syrian dictator Bashar al-Assad wants to break out of his strongholds in the west of the country – in part to deny Washington a bargaining chip in the event that US-backed forces hold Syria's south-eastern corner.

But there is evidence too that Iran has a grand design to take the same territory, to give it a "highway" from Tehran, through Iraq and Syria, to the Mediterranean – and that this effort is led by its most accomplished soldier and strategist, Qasem Suleimani, commander of the Quds Force.

As thousands of Iranian-backed Shiite militiamen, including a reported 3000-strong Hezbollah force from Lebanon, are being redirected from other battlefields in Syria and from the battle for Mosul in Iraq, Syria's south-east has become a magnet – not only through the presence of the Kurdish-led Sunni SDF, but also their US patrons, 150 of whom are stationed in the south-east, training and advising their proxies.

Success by General Suleimani's militias in driving Isis from the Iraqi border town of Baaj early in June has heightened speculation on Tehran's ambition.

From Baaj the route to the west would cross into Syria, possibly through the city of Deir al-Zor, where regime forces and a civilian population of 100,000 are besieged by Isis; and nearby Mayadeen, which is under Isis control.

But in pushing into Syria, the Iranian-backed forces have clashed three times with US forces and Washington's proxies near a town called al-Tanf.

All three encounters were described by Washington more as force protection than a deliberate opening of a new front. But the Americans reportedly have moved new rocket systems into the area and last week Pentagon spokesman Captain Jeff Davis issued a warning: "If [the Iranian-backed militias] resume their advance, coalition forces will defend themselves."

Parsi, author of the just published Losing an Enemy: Obama, Iran and the Triumph of Diplomacy, argues: "There seems to be an effort to drive things to a confrontation on the balance of power in the region without a public debate and with no input from Congress.

"And depending on how Russia responds [to Sunday's US air strike], this could become a very bad situation."

At the Centre for a New American Security, analyst Ilan Goldenberg worries that after staying out of each other's way, the Americans and the Iranians are in a race for the same territory – "and racing over the carcass of [Isis] creates all kinds of possibilities for tension, as we've witnessed in the last few weeks".

Observing that the stated US objective in Syria is the defeat of Isis, Goldenberg worries that an emerging US effort to block Iran's road to the sea is being executed in the absence of considered policy formulation.

He sees some merit in the idea, particularly as reassurance for the US's skittish Sunni allies in the region.

"There's a lot of poking and testing as Iran and Assad test the will of the US," he said. "But if there are clear US red lines, we're less likely to have miscalculations and to be able to control territory – ambiguity and the absence of a clearly stated objective makes direct confrontation more likely."

Ali Vaez, senior Iran analyst at the International Crisis Group, sees Iran's weekend missile strikes on Deir al-Zor "further complicating an already complex situation".

He said: "If there is one lesson from six years of war in Syria, it is that escalation on one side begets escalation from others. The Trump administration's pushback against Iran and its partners was bound to create a counter-action.

"Iran managed to kill multiple birds with one stone: it retaliated Isis's attack at the heart of its capital, defied new US sanctions against its ballistic missile program and sent a message of deterrence to Washington and its regional allies.

"If the US takes measures beyond rhetorical condemnation of Tehran's missile strikes, tensions could escalate too far too quickly."

Julien Barnes-Dacey, an analyst with the European Council on Foreign Relations, worries that the new US administration has not learnt the lessons of its predecessors in Iraq.

Barnes-Dacey writes: "A fight against Iranian proxies in eastern Syria is likely doomed to failure and would distract attention away from other important areas of the country. A US-supported push into eastern Syria will almost certainly end in failure given the regime and Iran's commitment to securing the area."

Then he gets really worried: "It also runs the risk of provoking a broader US-Iranian conflagration that would significantly set back any efforts to defeat [Isis] and secure some form of peace not just in Syria, but also in neighbouring Iraq."