Egypt expelled Turkey's ambassador on Saturday and Ankara downgraded relations in tit-for-tat moves, further fraying ties that soured after the July ouster of Islamist president Mohamed Morsi.
The latest row between the two US allies came after Turkish Prime Minister Recep Tayyip Erdogan on Thursday renewed his criticism of the "coup" that ousted Morsi and Egypt's continuing crackdown on his Islamist supporters.
Turkish officials initially expressed hope the differences could be resolved, but Erdogan appeared unbowed after the latest spat, saying: "I will never respect those who come to power after a coup."
Cairo expelled Turkish ambassador Huseyin Avni Botsali, declared him persona non grata, downgraded ties to the level of charge d'affaires and elected not to send back its ambassador to Ankara.
The foreign ministry accused Turkey of "supporting... organisations seeking to create instability in the country", a clear reference to Morsi's Muslim Brotherhood movement.
It said Ankara was "trying to influence the international community against Egyptian interests".
Turkey responded by declaring Egyptian envoy Abderahman Salah El-Din "persona non grata" and downgrading ties with Cairo "in line with the reciprocity principle that forms the basis of international relations".
The Turkish foreign ministry summoned the Egyptian charge d'affaires for an explanation and said Ankara held Cairo's new military-installed authorities responsible for the current tensions.
Turkish Foreign Minister Ahmet Davutoglu also criticised Egypt for leaking the decision to expel the ambassador to the media before consultations with the envoy were completed, calling it "behaviour that does not bode well with diplomatic courtesy."
"Diplomatic courtesy is observed even at times of crises between countries," he said, adding that the ambassador would return home "at the earliest opportunity".
Cairo and Ankara had both recalled their ambassadors after a previous spat in August. Botsali eventually returned to Cairo but Egypt's envoy stayed at home.
Egyptian foreign ministry spokesman Badr Abdelatty said Erdogan's comments earlier this week were "provocative" and amounted to "interference in Egypt's internal affairs".
Erdogan said on Thursday: "I applaud Mr Morsi's stance against the judiciary. I respect him. I have no respect for those who put him on trial."
Morsi is being tried on charges of inciting the killing of protesters during his turbulent one-year rule but has told the court he remains Egypt's legitimate president and does not recognise its authority.
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On Saturday, at a rally in northern Turkey Erdogan held up four fingers in a sign that has become associated with Egypt's violent dispersal of Islamist protesters in Cairo's Rabaa al-Adawiya square in August, in which hundreds of people were killed.
'Struggle for democracy'
Speaking to reporters, Erdogan said: "We have supported the struggle for democracy in the world. We never respect those who do not respect the people's sovereign rights."
"What matters to us is the strengthening of democratic parliamentary (systems) in the world."
Turkey's Islamist-rooted Justice and Development Party government forged an alliance with Morsi after he won Egypt's first free presidential election in June 2012.
A year later Morsi was toppled by the army after mass protests by opponents who accused him of poor governance and betraying the 2011 uprising that ousted president Hosni Mubarak.
Erdogan angered Egyptian authorities by describing Morsi's July 3 ouster as a "coup" and caused further outrage with repeated calls for his release.
The row escalated in August when Erdogan condemned the deadly dispersal of the pro-Morsi protest camps in Cairo, and later Egypt and Turkey recalled their ambassadors for consultations.
Earlier on Saturday, Turkish President Abdullah Gul sought to ease tensions, saying: "The situation between Turkey and Egypt is temporary and conjectural."
"Turkey and Egypt are just like two halves of an apple on the two sides of the Mediterranean. We're very sad about what's going on in Egypt. I hope relations will be back on track."
Morsi's ouster triggered international condemnation, which intensified after a crackdown on Islamists led to more than 1,000 deaths and more than 2,000 arrests.
Washington even suspended part its annual $1.5 billion military aid to its long-time ally.
Egypt's interior minister Mohamed Ibrahim on Saturday announced the arrest of dozens of "extremists" connected with deadly attacks and accused the Brotherhood of financing Islamists linked to Al-Qaeda.