Turkey admitted Monday there may have been some "unfair" treatment in its post-coup crackdown as it voiced anger with Germany for barring President Recep Tayyip Erdogan from addressing a rally in Cologne.

Retaliating after a military attempt to unseat him, Erdogan has launched a purge that has seen tens of thousands people suspended from their jobs and almost 19,000 detained.

Apparently responding to widening international alarm about the crackdown, Prime Minister Binali Yildirim admitted there may have been some unfair treatment in the state sector.

"There must definitely be some among them who were subjected to unfair procedures," he said in comments published by state-run Anadolu news agency.

"We will make a distinction between those who are guilty and those who are not."

Echoing his tone, Deputy Prime Minister Numan Kurtulmus said: "If there are any mistakes, we will correct them".

Turkey meanwhile summoned a senior German diplomat, a day after a rally of tens of thousands of Erdogan supporters in Cologne in opposition to the coup.

Hours before the demonstration, Germany's constitutional court rejected an application to show via video link live speeches from Turkey by politicians including Erdogan, over fears they could work up the crowd.

The decision sparked anger in Turkey, with presidential spokesman Ibrahim Kalin calling the move unacceptable and a "violation of the freedom of expression and the right to free assembly".

A spokeswoman for the German embassy told AFP that the charge d'affaires had "been summoned to the Turkish foreign ministry at 1:00 pm (1000 GMT)" on Monday over the rally.

But Germany, which is home to Turkey's largest diaspora, played down the incident, saying such "invitations" were nothing out of the ordinary.

"In the day-to-day dealings between countries, it is a daily event -- normal for a representative of a country to be called in to the foreign ministry of his host country," German foreign ministry spokesman Martin Schaefer told journalists.

Ties between Germany and Turkey are already strained over the German parliament's decision to brand as genocide the World War I-era Armenian massacre by Ottoman forces.

Turkish officials were also to meet with the top US military commander in the first direct talks since the failed coup, with Washington under pressure from Ankara to extradite the alleged mastermind, Islamic preacher Fethullah Gulen.

General Joseph Dunford, chairman of the US joint chiefs of staff, was to meet with Yildirim and Turkish chief of staff General Hulusi Akar.

"He will deliver messages condemning in the strongest terms the recent coup attempt and reaffirming the importance of our enduring partnership for regional security," Dunford's spokesman Greg Hicks said in a statement.

Tensions between the two NATO allies have been aggravated by the foiled putsch, with some Turkish officials even alleging that Washington could have had a hand in the plot. The suggestion has been firmly denied by top US officials.

Turkey is now requesting the extradition of Gulen -- who has lived in self-imposed exile since 1999 -- from his leafy compound in Pennsylvania.

"We do not want (the US) to be in a position that will make us question our friendship," Yildirim said.

"If they keep on dragging (their) feet on the Gulen issue... then things will take a different course, because the events of July 15 are crystal clear."

After a cabinet meeting in Ankara, Kurtulmus said Washington would have to choose between support for a "terrorist chief" and the citizens of Turkey.

Last week, Erdogan lashed out at the top US general in the Middle East, General Joseph Votel, after he expressed concerns about the future of military relations between the two allies in the wake of the putsch.

Meanwhile Turkey on Monday said it had arrested 11 fugitive soldiers suspected of involvement in an attack on Erdogan's hotel during the night of the coup.

Erdogan was staying in the western seaside resort of Marmaris on July 15 but dashed to Istanbul just before the hotel came under attack from rebel soldiers determined to oust him from power.

Just one soldier from the attack group now remains at large, Kurtulmus said.