United States Defence Secretary Ash Carter has reiterated his country's strong commitment to Turkey in the aftermath of a failed military coup which has raised question marks about the bonds between the two nations.

"Turkey has been a strong ally for decades," Mr Carter said, "and the relationship remains very strong."

But with around 100 generals and admirals - a third of Turkey's armed forces' top brass - now under arrest and the purge of judges, university lecturers and other Turkish civil servants reaching 60,000 since last Friday's coup, nobody in either Washington or Europe's capitals believes that Turkey's relations with its chief allies can remain unaltered.

For the anti-Western backlash inside Turkey is now in full swing, and appears to be led by Turkish President Recep Tayyip Erdogan.

Mr Erdogan always had a testy relationship with the US. He neither forgot nor forgave Washington's tacit support for previous coups mounted by the Turkish military during the 1970s and 1980s. But at the same time, he was also eager to capitalise on his country's pivotal strategic role within the US-led Nato alliance.

Yet even before last week's coup, this delicate balancing act was fraying. During a visit to Washington in March, Mr Erdogan was infuriated by his persistent inability to secure a high-profile meeting with President Barack Obama. To show his displeasure, he gathered the heads of US think-tanks for a dinner during which, according to a person who was there, he "pretty much threw the administration under a bus".

Mr Erdogan also resented his country's growing marginalisation in the Middle East, which he blamed on the US administration's growing preference for consulting Russia. Increasingly, however, Turkish-US ties were overshadowed by the presence on American soil of Turkish cleric Fethullah Gulen, accused by the Turkish authorities of masterminding last week's failed coup.

Pro-Erdogan supporters waving Turkish national flags during a rally at Taksim square in Istanbul on Wednesday, following the failed military coup attempt of the previous week. PHOTO: AGENCE FRANCE PRESSE

The two men were once close allies; ironically, the US used to be criticised in the past by Turkey's secular opposition parties - which are Mr Erdogan's enemies - of not doing enough to silence the cleric. But after the two fell out in 2013, it is the Turkish government which blames Washington for shielding him.

The Americans feared all along that they would be accused of being behind last week's failed coup; in a nation which thrives on conspiracy theories, the US, the European Union and Israel are routinely accused of being behind almost anything that happens in Turkey.

Still, Washington was taken aback by the readiness of top Turkish officials to push such conspiracy theories: Turkish labour minister Suleyman Soylu publicly claimed that "the US is behind the coup attempt" and even Mr Erdogan talked about "other countries which may have been implicated", a none-too-subtle reference to the US.

Nato officials also noted with concern Mr Erdogan's decision to cut off electricity supplies to the Incirlik Air Base in southern Turkey, a sprawling military facility which serves as the staging point for US operations against Islamic State in Iraq and Syria militants; the electricity "lockdown" continues almost a week after the coup, a sure sign that it is intended as a warning to Nato and the US.

But the most puzzling development is Mr Erdogan's claim to be fighting a vast "terrorist network" called Feto (Fethullah Terrorist Organisation) and led by Mr Gulen. No Western intelligence agency has ever heard of such an organisation, although Turkish officials claim that it has "tens of thousands" of supporters, more than Al-Qaeda and ISIS put together.

The fear in many Western capitals is that the mass arrests in Turkey are not about eradicating terrorism, but about marginalising Mr Erdogan's political opponents, and that the result will be long-term damage to the efficiency of Turkey's armed forces, among Nato's most capable. It is already clear that the Turks will need a generation to replace the officer corps Mr Erdogan has decimated.

European countries are not in a good position to criticise Mr Erdo- gan's decision to declare a "state of emergency" for the next three months; after all, France has had a similar state of emergency since last November.

Still, talk of the restoration of the death penalty in Turkey worries European governments, if only because such a move will impose a legal freeze on Europe's ties with Turkey for years if not decades to come.

For the moment, both the US and European governments are desperate to avoid criticising Turkey in public. But patience with the Turks is wearing thin: as US Secretary of State John Kerry pointedly remarked earlier in the week, Nato, of which Turkey has been a member since 1952, will "measure very carefully what is happening".