Ties between the United States and one of its most crucial military allies, Turkey, were rapidly fraying Monday as Washington criticized the widespread purges that have followed an abortive coup d'état, and Turkey's Prime Minister said there would be "a questioning of our friendship" if the U.S. didn't extradite the man Ankara believes masterminded the failed putsch.

At the centre of the drama is Fethullah Gulen, a retired imam who Turkish President Recep Tayyip Erdogan says was behind the coup attempt that saw a faction of the army and air force take over strategic locations in Istanbul and Ankara on Friday, only to surrender them when Mr. Erdogan called his supporters into the streets a few hours later. At least 300 people died in the brief but ferocious fighting, which saw soldiers use live ammunition on pro-government protesters and the parliament building in Ankara bombed from the air.

Mr. Gulen, who was an ally of Mr. Erdogan's until 2013, now lives in self-imposed exile in Pennsylvania. Turkey, which accuses Mr. Gulen's followers in the police, army and judiciary of building up a "parallel state," is demanding that the U.S. extradite the cleric immediately to face trial.

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U.S. Secretary of State John Kerry said that will only happen if Turkey can provide evidence of Mr. Gulen's involvement that would withstand the scrutiny of a U.S. court. That answer provoked fury here.

Many Turks feel that American forces stationed on the southern Incirlik air base, from which the U.S.-led coalition is flying missions against Islamic State, could have and should have stopped a refuelling plane which supported the coup plotters' air force from taking off. Many Turks also believe the Obama administration waited several hours as events evolved on Friday before making a statement in support of Turkey's democracy because it was wavering about supporting the coup.

"We would be disappointed if our [American] friends told us to present proof even though members of the assassin organization are trying to destroy an elected government under the directions of that person," Prime Minister Binali Yildirim said Monday, referring to Mr. Kerry's request for evidence of Mr. Gulen's involvement in the coup plot. "At this stage there could even be a questioning of our friendship."

The battle over Mr. Gulen's fate unfolded in parallel with another very public argument between the American and Turkish governments over a widespread purge of Mr. Erdogan's opponents that began just hours after the coup collapsed.

More than 7,500 members of the military, police and judiciary – including 27 generals and admirals, as well as Mr. Erdogan's own chief military adviser – have been detained since Saturday. Almost 9,000 others, including 30 local governors, have been removed from their posts.

The crackdown shows no sign of slowing. On Monday, the government suspended some 1,500 finance ministry officials. It also cancelled annual leave for the country's three million civil servants, demanding that those already on vacation return immediately to their posts. Public officials were also banned indefinitely from travelling abroad.

Mr. Erdogan's government also appears to have zeroed in on former air force chief Akin Ozturk as a co-leader of the coup. The state-run Anadolu agency reported on Monday that Mr. Ozturk had confessed, though other outlets later contradicted the story.

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Mr. Ozturk and the other high-ranking suspects were paraded for the cameras on Monday. Mr. Ozturk's right ear had a large bandage on it, and there were red marks on his face and neck. The other prisoners also appeared to have been beaten.

Mr. Kerry appeared to suggest that even Turkey's membership in North Atlantic Treaty Organization could come under review if the purge was deemed to go too far. "NATO also has a requirement with respect to democracy, and NATO will indeed measure very carefully what is happening," he told reporters in Brussels on Monday.

Any move to reconsider Turkey's place in the 28-member alliance would be a tectonic geopolitical shift. Turkey boasts NATO's second-largest standing military, after the U.S., and its efforts are seen as crucial to both combatting the so-called Islamic State that occupies parts of neighbouring Syria and Iraq, as well as to controlling the flow of refugees trying to reach Europe.

Underscoring how tense the relationship between Washington and Ankara has become, White House spokesman Josh Earnest said Monday that Mr. Obama had not had an opportunity to speak to Mr. Erdogan since the coup attempt. Meanwhile, Turkey's Foreign Minister Mevlut Cavusoglu said any criticism of how the government treated coup suspects was tantamount to backing for the overthrow bid.

"This entire plan was organized from Pennsylvania. Our Western friends seem to be in support of Fethullah," Yasin Aktay, the deputy chairman of Mr. Erdogan's Justice and Development Party (better known by its Turkish acronym AKP), told The Globe and Mail. "They now have to take a side. Will France and America side with someone who is sabotaging Turkish democracy? Or will they side with the Turkish people?"

Mr. Gulen has denied any involvement in the plot and suggested instead that it was orchestrated by Mr. Erdogan in order to justify the subsequent crackdown.

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A thirst for revenge lingered Monday on the streets of Istanbul, where thousands of demonstrators again rallied on central Taksim Square to show their support for Mr. Erdogan's government. They chanted for a second straight night in support of Turkey reinstating the death penalty, and Mr. Erdogan told CNN that he would support such a change if it was first passed by the AKP-dominated parliament.

"The people on the streets have made that request," Mr. Erdogan said. "The people have the opinion that these terrorists should be killed. … Why should I keep them and feed them in prisons for years to come, that's what the people say."

In an interview with CNN broadcast late Monday, Mr. Erdogan said that he escaped death by only a few minutes before coup plotters stormed the resort in southwest Turkey where he was vacationing last weekend and killed two of his bodyguards.

"Had I stayed 10, 15 additional minutes, I would have been killed or I would have been taken," he told CNN through a translator provided by the presidency.

European Union foreign policy chief Federica Mogherini said a move to reinstate capital punishment – which Turkey abolished in 2004 – would effectively bring an end to 11 years of negotiations over Turkey's potential membership in the EU. "No country can become an EU member state if it introduces the death penalty," she said in Brussels.

Mehmet Solmaz, news editor at the pro-government Daily Sabah newspaper, said such warnings were unlikely to sway Turkish public opinion.

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"A colleague of mine read [the EU statement] out loud and everybody just said 'Damn the EU accession,'" Mr. Solmaz said in an interview. "People need to understand that this country has witnessed a coup and there are going to be consequences. Anyone who was involved in any way is going to pay a price. If you want to call it a witch hunt, so be it."

With a report from Associated Press