Good news about Syria is so rare that the recent announcement that the United Nations is setting up a special investigation into chemical weapon use is especially welcome. The hope must be that this might prevent more chemical atrocities – which haven’t stopped, despite diplomatic efforts. But the much less positive backdrop is that Russia has made sure any UN text aimed at establishing responsibility will shield Syria’s regime from accountability: Russia will use veto power if need be. This is in line with Vladimir Putin’s overall strategy, which has always been to protect the Assad regime from any UN security council action against the large-scale killing of civilians his forces have been carrying out.

Now there are reports that Russia is setting up a military base in Latakia, on Syria’s coast. The official explanation is anti-terrorism and countering Islamic State – a formula that, on the face of it, aligns Russia with western objectives. The most optimistic take is to say that Russia is now anticipating a grand international bargain over Syria, to end the war while possibly carving up the country into zones of influence. There are signs Russia is worried about a US-Iran rapprochement on Syria that might diminish its clout. It is no coincidence that the new military base is in the heart of Alawite territory, Bashar al-Assad’s core constituency.

The deployment could give Moscow more of a say in an eventual negotiation, especially after Mr Assad’s forces have apparently been losing ground in the southern parts of Syria. The less optimistic view is that the Syrian war is destined to grind on much longer – beyond a death toll that now stands at a quarter of a million – and Russia is simply making sure its ally has the forces, the munitions and whatever other support he needs to hold on.

Such developments draw less international public attention than the flow of refugees into Europe. Yet they weigh heavily on what may lie ahead. Russia and Iran are Mr Assad’s key backers. Anyone wondering why tens of thousands are fleeing Syria must remember that the vast majority of civilian casualties have been caused by his forces, and the militias that assist them. The scale of these crimes has been well documented, from barrel bombs dropped by helicopters on cities, to indiscriminate artillery fire and the disappearance of tens of thousands of Syrians in torture centres. How he continues to finance his military machine despite international sanctions and a collapsed economy is a question that no doubt points to money and other assistance coming from Russia and Iran. This is not to say that horrible war crimes have not been committed by jihadi rebel groups. But they account for a much smaller share of casualties.

So, when debating the Syrian war, it is important to discriminate between the various external state involvements. There are so many actors that it has become tempting to think responsibility for the death toll and the human misery are equally shared by the west, Saudi Arabia, Russia, Iran, Turkey and others.

Look more closely at the dynamics of the war and it becomes obvious that some actors are much more implicated – directly or indirectly – in the massacres of civilians. Russia has a special responsibility, not only because it is Mr Assad’s most powerful backer but because, unlike Iran, it holds a permanent seat on the UN security council.

This is why, as Mr Putin heads for the UN general assembly in New York later this month, efforts to adopt a resolution banning the use of barrel bombs must stay focused. Russia will undoubtedly veto such a text, but that would at least expose its complicity. The Syrian quagmire has taken on such a degree of complexity, and western governments are now so intent on just combatting Isis, that it has become commonplace to say there is nothing left to do about Syria but targeted counter-terrorist air strikes, along with increased aid for refugees.

It says a lot about western strategic disarray in the Middle East that this policy suits both the Assad regime and Russia well. This will not do anything to save lives, nor to stop the outflow of Syrian families to Europe. There is no clear-cut solution to this war, and perhaps never has been, but as things now stand, western states are missing a key point: when the UN general assembly gathers, Mr Putin should not be given the chance to bask in anti-Isis solidarity with the west as if he had no role in Syria’s killing fields. Strong pressure must be brought to bear on him, because he is Mr Assad’s chief patron, and Mr Assad is the number one cause of deaths in Syria.