The disastrous miscalculation made by the United States in signing a military agreement with Turkey at the expense of the Kurds becomes daily more apparent. In return for the use of Incirlik Air Base just north of the Syrian border, the US betrayed the Syrian Kurds who have so far been its most effective ally against Islamic State (Isis, also known as Daesh). In return for this deal signed on 22 July, the US got greater military cooperation from Turkey, but it swiftly emerged that Ankara’s real target was the Kurds in Turkey, Syria and Iraq. Action against Isis was almost an afterthought, and it was hit by only three Turkish airstrikes, compared to 300 against the bases of the Kurdistan Workers’ Party (PKK).

President Barack Obama has assembled a grand coalition of 60 states, supposedly committed to combating Isis, but the only forces on the ground to win successive victories against the jihadis over the past year are the ruling Syrian-Kurdish Party (PYD) and its People’s Protection Units (YPG). Supported by US air power, the YPG heroically defeated the Isis attempt to capture the border city of Kobani during a four-and-a-half month siege that ended in January, and seized the Isis crossing point into Turkey at Tal Abyad in June.

The advance of the Syrian Kurds, who now hold half of the 550-mile Syrian-Kurdish border, was the main external reason why Turkish President Recep Tayyip Erdogan offered the US closer cooperation, including the use of Incirlik, which had previously been denied. The domestic impulse for an offensive by the Turkish state against the Kurds also took place in June when the pro-Kurdish People’s Democratic Party (HDP) won 13 per cent of the vote in the Turkish general election, denying Mr Erdogan’s Justice and Development Party (AKP) a majority for the first time since 2002. By strongly playing the Turkish nationalist and anti-Kurdish card, Mr Erdogan hopes to win back that majority in a second election on 1 November.

There are signs of a growing understanding in Washington that the US was duped by the Turks, or at best its negotiators deceived themselves when they agreed their bargain with Ankara. Senior US military officers are anonymously protesting in the US media they did not know that Turkey was pretending to be going after Isis when in practice it was planning an offensive against its 18 million-strong Kurdish minority.

A female fighter from the Kurdish People Protection Unit (YPG) (AFP)

Further evidence of misgivings in Washington came last week with an article in The New York Times entitled “America’s Dangerous Bargain with Turkey” by Eric S Edelman, former US ambassador to Turkey and under-secretary for defence policy, who is normally regarded as a neo-con of good standing. He accuses Mr Erdogan of unleashing “a new wave of repression aimed at Kurds in Turkey, which risks plunging the country into civil war” and he goes on to suggest that this might help the AKP win back its majority, but will certainly undermine the fight against Isis. He says: “By disrupting logistics and communications between the PKK in Iraq and the PYD in Syria, Turkey is weakening the most effective ground force fighting the Islamic State in Syria: the Kurds.”

In fact, there is growing evidence that the Turkish government has gone even further than that in weakening US allies opposing Isis in Syria, Arab as well as Kurd. For several years the US has been trying to build up a moderate force of Syrian rebels who are able to fight both Isis and the Syrian government in Damascus. The CIA-run initiative has not been going well because the Syrian military opposition these days is almost entirely dominated by Isis, which holds half Syria, the al-Qaeda affiliate Jabhat al-Nusra, and the equally sectarian Sunni Ahrar al-Sham.

But in July, the US plan to create such a moderate force was humiliatingly knocked on the head when Jabhat al-Nusra attacked and kidnapped many of this US-trained force as they entered Syria from Turkey. It now seems certain that Nusra had been tipped off by Turkish intelligence about the movements of the US-backed unit known as “Division 30”. Turkey apparently did this because it does not want the US to have its own surrogate in Syria. According to an investigation by Mitchell Prothero of the McClatchy news organisation, citing many Syrian sources in Turkey, the Turkish motive was to destroy the US-run movement, which was intended to number 15,000 fighters targeting Isis. Its disintegration would leave the US with no alternative but to train Turkish-sponsored rebel groups whose primary aim is to topple Syria’s President Bashar al-Assad. The article quotes a Syrian rebel commander in the Turkish city of Sanliurfa, 30 miles north of the Syrian border, as saying that the Turks “don’t want anything bad to happen to their allies – Nusra and Ahrar al-Sham – along the border, and they know that both the Americans and the Syrian people will eventually recognise that there’s no difference between groups such as Nusra, Ahrar and Daesh.”

How does Isis itself assess the new US-Turkish accord? Its fighters may find it more difficult to cross the Syrian-Turkish border, though even this is uncertain. But it will be relieved that its most effective enemy in Syria, the PYD, will in future be restrained by Turkish pressure. Its PKK parent organisation is coming under sustained attack from Turkish forces in south-east Turkey and in the Qandil Mountains of Iraq.

In pictures: Fighting between Kurds and Isis intensifies in Kobani Show all 30 1 /30 In pictures: Fighting between Kurds and Isis intensifies in Kobani In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani An explosion rocks Syrian city of Kobani during a reported suicide car bomb attack by the militants of Isis group on a People's Protection Unit (YPG) position in the city center of Kobani, as seen from the outskirts of Suruc, on the Turkey-Syria border In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani An explosion rocks the Syrian city of Kobani during a reported suicide car bomb attack by Isis Getty In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani An explosion in the Syrian city of Kobani set off as fighting continues Getty Images In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Heavy smoke rises following an air strike by the US-led coalition aircraft in Kobani Getty Images In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani An unidentified armed man takes position near a building in the Syrian town of Kobani, as seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Kurdish fighters walk to their positions in Kobani In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Residents of Kobani walk in the streets of the besieged town, as seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani People's Protection Unit (YPG) fighters walk in the Syrian town of Kobani, as seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani People watch the Syrian town of Kobani from near the Mursitpinar border crossing, on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani A Turkish soldier stands on a top of a tank as he watches the Syrian town of Kobani from near the Mursitpinar border crossing, on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises from the Syrian town of Kobani, seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc. Kurdish forces defending Kobani urged a U.S.-led coalition to escalate air strikes on Isis fighters who tightened their grip on the Syrian town at the border with Turkey. A group that monitors the Syrian civil war said the Kurdish forces faced inevitable defeat in Kobani if Turkey did not open its border to let through arms, something Ankara has appeared reluctant to do In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Newly arrived People's Protection Unit (YPG) fighters walk in a line in the Syrian town of Kobani, seen from near the Mursitpinar border crossing on the Turkish-Syrian border In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Heavy smoke rises from the Syrian town of Kobani, seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Kurdish women mourn at the grave of a relative, who was a Kurdish fighter killed in fighting with the militants of the Islamic State group in Kobani, and was buried at a cemetery in Suruc In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Turkish army tanks mechanized units take position on top of a hill near Mursitpinar border crossing in the southeastern Turkish town of Suruc in Sanliurfa province In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises after an US-led air strike in the Syrian town of Kobani. The air strikes pushed Isis fighters back to the edges of the Syrian Kurdish border town of Kobani, which they had appeared set to seize after a three-week assault, local officials said In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani A huge plume of smoke rises after an airstrike in eastern Kobani, Syria, behind a hilltop where militants with the Islamic State group had raised their flag on Monday AP In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Turkish Kurds watch as airstrikes hit Kobani AP In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises from the Syrian town of Kobani as Turkish army tanks take position on the Turkish side of the border Reuters In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Military aircraft flies over the Turkey-Syria border as it nears targets in Kobani In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises after a US-led air strike in the Syrian town of Kobani Reuters In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Turkish Kurds, on the Turkey-Syria border, watch over the border at the intensified fighting between Isis and Kurdish forces AP In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises during airstrikes on the Syrian town of Ain al-Arab, known as Kobani by the Kurds Getty In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani A huge plume of smoke rises after an airstrike outside west Kobani, Syria AP In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani A militant with the Isis group walks in the town of Kobani In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Militants with the Isis group, bottom, along with a machine gun-fitted pick up truck, partially seen bottom right, hold positions in Kobani, during intensified fighting with Syrian Kurds In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani People watch smoke rising from the Syrian town of Ain al-Arab, known as Kobani by the Kurds, after an air strike Getty In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Smoke rises from a strike at an area of a mosque that destroyed its minaret, in Kobani during heavy fighting between militants with the Isis group and Syrian Kurds In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani Militants with Isis hold positions in Kobani, Syria, during intensified fighting with Syrian Kurds AP In pictures: Fighting between Kurds and Isis intensifies in Kobani Kobani A partial view of Kobani with a mosque's minaret

The destruction of one of the most famous temples at Palmyra by Isis last week, and the decapitation of the site’s most famous archaeologist a few days earlier, are a show of strength and acts of defiance very much in the tradition of the Islamic State. The aim is to dominate the news agenda, which can easily be done by some spectacular atrocity, and thereby say, in effect, “you may hate what you are seeing, but there is nothing you can do to stop it”.

And this is demonstrably the case not just in Syria but in Iraq. Isis captured Ramadi, the capital of Anbar province in Iraq on 17 May and Palmyra five days later on 22 May. In neither case has there been an effective counter-attack. Isis is still winning victories where it counts, and faces no real threat to its existence.

The US campaign against Isis is failing and the US-Turkish deal will not reverse that failure and may make it more complete. Why did US negotiators allow themselves to be deceived, if that is what happened. No doubt the US air force was over-eager for the use of Incirlik so it would not have to fly its planes from Jordan, Bahrain or carriers in the Gulf.