Public accountability will be negatively affected with cumbersome rules for indicting the President for suspected abuse of power.
Sanders said that the president was not supporting or accepting the results of the referendum, congratulating Erdogan more as a formality, and that the phone call did not signal an endorsement or acceptance of the voting results.
As someone who watches Turkey closely, I can say that the Erdogan regime had to pressurise the YSK to take these frantic measures to save the day for them because they themselves did not expect such a close result.
"Therefore we do not have any difficulties on that front", Erdogan said.
Voting was already underway on Sunday when the electoral authority announced it would start accepting unstamped ballots - a decision that the opposition said should invalidate the results.
Royce said he was troubled by the observers' initial reports of irregularities and would review the full report when released.
Observers from the Organization for Security and Cooperation in Europe (OSCE) and the Council of Europe said Sunday's referendum had been an uneven contest.
The question everyone asks now is if Turkey will develop into a stable, governable and inclusive democracy or if President Erdoğan will interpret the outcome of the referendum, despite the slim majority it granted him, as the "will of the people" to govern in its name and disregard the opinions and rights of the other half.
Critics argued the reforms were tantamount to creating an elected dictatorship, while Erdogan and his supporters said they would create a fast and efficient system of government better able to confront terrorism and a sluggish economy.
Germany is Turkey's most important trading partner, with a total volume of 37 billion euros ($39 billion), and one of its largest sources of foreign investment.
Kempf said Tuesday that Turkey "needs a strong business partner in Europe that supports the further economic development of the country".
Videos have emerged in Turkey of alleged ballot stuffing and polling station violations during the Sunday referendum that approved sweeping powers to the country's president.
The constitutional amendments also end the official neutrality of the presidency, allowing a president to lead a political party and declare states of emergency.
He claims his extended powers have not changed him, and had called out European Union officials who he says have broken promises when it comes to Turkey's membership. "This is the reddest of all red lines".
Turkey hopes ties with the Trump administration will improve after relations soured between the North Atlantic Treaty Organisation allies during Barack Obama's term over Syria and Turkey's calls for US-based Muslim cleric Fethullah Gulen to be extradited.
But Binali Yildirim warned that calling for street protests was unacceptable. Turkey's prime minister on Tuesday called on the opposition to respect the result of a referendum that will give sweeping new powers to the office of the president, but the main opposition party formally requested the vote be annulled.
Turkey's Supreme Electoral Board (YSK) made a controversial last-minute decision on April 16 to count ballots that had not been stamped by officials.