The US, Britain and France have all strongly criticised the Turkish invasion of northern Syria, but the three countries have so far been unwilling to instruct their Nato partner to pull back.

The low-key stance urging Turkey to minimise casualties probably means Ankara can press ahead with its attempts to drive the Syrian Kurds out of Afrin province in north-west Syria.

The problem for the west is that, as an endgame possibly approaches in Syria, it cannot afford to lose Turkish diplomatic support since Ankara has been the vital countervailing force to a Russian-imposed peace.

The Turkish preoccupation with the Syrian Kurds on its borders could lead to the Turkish president, Recep Tayyip Erdoğan, reaching a deal with Damascus and Moscow.

US military to maintain open-ended presence in Syria, Tillerson says Read more

That would represent a disaster for the US only a week after the US secretary of state, Rex Tillerson, committed the Trump administration to a political solution in Syria that involved the ultimate removal of Bashar al-Assad and Iranian-led militias.

The speech – in which the UK Foreign Office had a big hand – was something of a watershed and was under-appreciated in Europe. Previously, Trump’s policy on Syria was simply the destruction of Isis and an aversion to talk of nation-building. But the Tillerson speech has been widely criticised because it was long on aspiration but short on detailing the credible levers the US and the west have to pressure Moscow to abandon Assad.

Western diplomats say they have some stakes in the ground: the threat to withhold EU and US reconstruction funds, the promise to keep 2,000 US troops inside Syria indefinitely and a slightly confused commitment to help the Kurds form a border force inside northern Syria. British ministers also repeatedly warn that a Russian-imposed peace that simply leaves Assad in charge would not only be morally reprehensible but unstable.

But the value of all these levers is immeasurably diminished if they lack the support of Turkey, the long-term supporter of the Syrian opposition in the seven-year civil war.

If Turkey instead sides with Moscow, Russia will be able to press ahead with its political solution for Syria to be launched at the Syrian National Dialogue Congress, an event co-sponsored by Turkey and Iran and due to be held in the Black Sea resort of Sochi on 29-30 January.

The west fears Vladimir Putin regards Sochi as an alternative to the UN-led peace talks, and an assertion of Russian authority across the Middle East. It could also be a means of rubber-stamping an agreement that leaves Assad in charge with some minor changes to the Syrian constitution.

In an attempt to retain the primacy of the UN process and achieve a broadly acceptable long-term political outcome, the UN’s special envoy for Syria, Staffan de Mistura, is to hold two sessions of talks either side of Sochi, the first on 25-26 January.

The Sochi conference has repeatedly been postponed by Moscow, mainly because Turkey has objected to any invitation being extended to the Kurdish Democratic Union party (PYD) and its armed wing, the People’s Protection Units (YPG). Turkey regards the YPG as inextricably linked to the Kurdisstan Workers’ party inside Turkey.

But the events of the past few days suggest Turkey and Russia may be close to a deal. Turkish military officials travelled to Moscow ahead of the Turkish invasion to extract guarantees that the Russian air force inside Syria would not attack Turkish units. On Monday Moscow then announced that Kurdish representatives would be invited to Sochi, without detailing the precise identity of those delegates.

The outlines of a deal are discernible – in which Turkey backs a Russian peace process and Moscow tacitly accedes to a Turkish drive to weaken the Syrian Kurds on its borders.

The US can argue it tolerated Kurdish territorial expansions across northern Syria, and specifically west of the Euphrates river, only so long as the Kurdish militias inside theSyrian Democratic Forces were needed to defeat Isis, but now that battle has been won the US priority is to stop the freefall in its relations with Turkey. If that means a temporary Turkish foothold in the patchwork that is Syria, so be it.

