WHEN news broke of a deal between Turkey and America over Syria last weekend, it was welcomed as a game-changer. But it has speedily become clear that the agreement is riddled with ambiguity and divergent agendas. That should not come as a surprise: the idea that two countries with such a fraught recent relationship were burying their differences to defeat Islamic State (IS) was always unlikely.

The apparent change of heart in Ankara came after the murder of 32 young activists at a Kurdish cultural centre in the border town of Suruc on July 20th. Having long turned a blind eye to IS (and other Sunni jihadist groups fighting Bashar Assad’s regime in Syria), the Turkish government seemed to have been shocked out of its complacency about the menace it poses.

In fact, Turkey had been edging towards taking a more active role in the coalition against IS for several weeks, which may well have been the trigger for the suicide attack. The reasons included growing alarm about the strengthening relationship between the Americans and the Kurds; active recruiting by IS inside Turkey’s big cities; and worry over the damage being done to Turkey’s reputation by its tolerance of IS. In June Barack Obama publicly criticised Turkey for failing to stem the flow of foreign fighters and arms across its border into Syria.

Although the details of the deal remain sketchy, Turkey has agreed to two long-standing demands from Washington. The first was to allow American warplanes to fly strike missions against IS positions from the big NATO airbase at Incirlik. With far less flying time to IS-held territory than from bases in the Gulf, aircraft can spend more time over their targets, respond more rapidly to real-time information from surveillance drones and maintain a higher tempo of operation. The second demand was that Turkish F-16 bombers would now join the coalition effort against IS.

In return, the Americans agreed to help establish a 65-mile IS-free zone along a western section of the Turkish-Syrian border, running from north of Aleppo to the Euphrates. That helped Ankara save face, but it is not the no-fly zone that the Turks have been demanding since the civil war in Syria erupted. That was intended to create a haven from the forces of Bashar Assad, particularly his aircraft, whereas the aim of this zone is merely to exclude IS.

In briefings earlier this week, the Turks expressed the hope that the zone would eventually provide a refuge for some of the 1.8m Syrian refugees in Turkey. Before that, though, the main aim of pushing IS out of the area is to sever the access-route to Turkey through which it funnels foreign recruits. As quickly as air strikes have killed the militants (about 1,000 are thought to be dying every month) replacements have filled their shoes. Having lost one crossing in the east at Tel Abyad to the Kurds in June, IS relies on another one, further west, Jarabulus, which is in the zone (see map).

The Turks hope for other benefits for themselves. As well as making this an IS-free zone, they would like to make it a Syrian Kurd-free zone as well, thwarting the Kurds’ plan to seize the contiguous territory they need to carve out a self-governing entity on Turkey’s frontier akin to the more or less autonomous Kurdistan in northern Iraq. That is a prospect that Turkey’s president, Recep Tayyip Erdogan (pictured, left) still fears far more than IS’s potential for mayhem. Although Turkey’s declared Syria strategy has been all about getting rid of Mr Assad, its support for the jihadists has always been at least as much about keeping the Kurds in check.

The real target

That fact can be seen from the targets chosen by the Turkish air force in the past few days. It has carried out some limited strikes against IS in north-west Syria, but it has shown more zeal in pounding positions held by the supposedly separatist Kurdish Worker’s Party (PKK) in northern Iraq, ending a two-year ceasefire against one of IS’s fiercer foes. The Turks are not bombing IS in Syria’s Euphrates valley, where it is fighting Syrian Kurd YPG militias. (The YPG is the armed wing of Syria’s Kurdish Democratic Union, an offshoot of the PKK.) Yet American planes are flying in support of YPG units fighting IS near Tel Abyad.

The Americans, who worked closely with the YPG during last year’s bitter defence of Kobane, rate the Kurdish militia as their most reliable ally against IS on the ground in Syria and intend to increase co-operation. The Turks say that although they regard the PKK as a terrorist organisation, just like IS, they have no plans to go after the YPG. However, there are reports (denied in Ankara) of Turkish tanks shelling YPG positions this week close to Jarabulus. A proven Turkish attack against the YPG would cross a red line, warn American officials. Yet for all its heroics in areas it seeks to control, the YPG is not going to take the fight to IS’s stronghold in Raqqa. For that, the coalition almost certainly needs to include Sunni Arabs.