At about 5pm on Saturday, two US F-16 fighter bombers and two A-10 specialised ground attack aircraft bombed what they believed was a concentration of Isis fighters besieging pro-government forces in the city of Deir Ezzor in eastern Syria.

Whoever it was in the US Air Force who had misidentified the target as Isis made a disastrous error; the US planes were attacking Syrian Army soldiers fighting Isis at a position called Jebel Tharda close to Deir Ezzor airport. The city has been besieged by Isis for over a year and 110,000 civilians are trapped inside. By the time the US bombing raid was over it had killed at least 62 Syrian soldiers and injured another 100, enabling Isis to overrun the survivors before being forced to retreat by a counter-attack backed by Russian airstrikes.

The mistake and heavy Syrian Army casualty list symbolises the continuing failure to implement the agreement reached between the US and Russia on 10 September. Its main points are a ceasefire in Syria, the unimpeded entry of UN aid convoys into besieged areas, and a joint US-Russian air campaign against Isis and Jabhat al-Nusra, the former Al-Qaeda affiliate in Syria relabelled as the Jabhat Fateh al-Sham. Of these requirements only an increasingly shaky ceasefire is in place so far.

Worse, the US and Russia are belabouring each other at the UN Security Council in New York, with the Russians accusing the US of complicity with Isis and the US claiming that Russia is opportunistically taking advantage of a targeting error for which the US has apologised. The Russian Foreign Ministry said today that the whole ceasefire accord, agreed after 10 months of negotiations between the two biggest players in the Syrian conflict, is close to unravelling.

Syria war: Heavy fighting ahead of ceasefire

The strength of the agreement should be that it was put together by the US, as the world’s sole superpower, and Russia, which aspires to that status. Each should be able to influence allies and proxies into implementing the ceasefire, but so far this is not happening. There are many armed clashes and 40 trucks filled with supplies for the 250,000 to 275,000 people trapped in rebel-held East Aleppo are still stuck on the Turkish border. Supposedly moderate US-backed rebel groups are meant to be separating themselves geographically from al-Nusra, but they remain intermingled with it.

A weakness of the agreement is that it lacks any mechanism for its implementation other than the enforced assent or goodwill of the multitude of parties involved in the Syrian conflict. Goodwill has always been in notably short supply in Syria since many of the players, both regional and local, have an interest in the war continuing, even though they may hypocritically pretend otherwise. It is still unclear how far the US and Russia are able to force their allies into line and how far they are pulling their punches in doing so.

The US can put pressure on the Syrian rebels to abide by a ceasefire by leaning on their outside backers in Turkey, Saudi Arabia and Qatar, but will this pressure be enough? In less than two months the US presidential election will produce a different occupant of the White House, who may have a new Syria policy. Not only is the present administration the lamest of ducks during this period, but it is more or less openly divided on the merits of a deal with Russia.

It is much in the interests of Russia to make this deal work, but it has difficulty in getting President Bashar al-Assad to do what it wants, even if he is militarily reliant on it. In the longer term, nobody quite knows in the present day Middle East the real political and military strength of rival powers. Before the US invasion of Afghanistan in 2001 and Iraq in 2003, there was excessive idea in the region of American omnipotence. Failure of the US to get its way in either war despite prolonged military engagement led to excessive idea of US weakness. Russia was likewise written off by the rulers of Gulf States up to the time it became the main foreign support of Assad and started behaving like a superpower again.

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It is too early to write off the present ceasefire, if only because the conflict in Syria is so long-standing and intractable that it was always going to be extraordinarily difficult to de-escalate. A price has to be paid for the way in which it was misunderstood and mishandled in the years after 2011 so it will take time to put out the fires allowed to blaze out of control for five years. The US-Russian agreement is the first truly serious attempt to reduce the violence and, crucially, it is between the heaviest hitters in the crisis and the only ones capable of bringing it to an end.

Other peculiarities dog the present agreement. It is directed against al-Nusra and asks for the “moderate” armed opposition to separate themselves from the jihadis. It has always been centrepiece of Western policy in Syria that there is such a powerful group of armed moderates – despite much evidence to the contrary. If they did exist in any force then this agreement would be much in their interests and they – like the Syrian Kurds, Iraqi Kurds and Iraqi Army – would find their firepower vastly increased by the help of the US Air Force. But if the moderates so-called are largely a myth, and the armed opposition is overwhelmingly dominated by Isis and al-Nusra, then the latter have every incentive to make sure that this ceasefire fails.