President Erdogan and his supporters say the "Turkish style" presidential system will bring stability and prosperity in a country rattled by last year's coup attempt and a series of devastating attacks by the so-called Islamic State group and Kurdish militants. Many global observers decried the results, suggesting that the referendum had not taken place on a level playing field.
In a newspaper interview, German foreign minister Sigmar Gabriel said that if Ankara were to bring back the death penalty as Erdogan had suggested, the move would be "synonymous with the end of the European dream".
The constitutional reforms are set to grant more powers to Erdogan, effecting a changeover from parliamentary to the presidential form of government in Turkey.
On Monday, worldwide election monitors delivered a scathing verdict on the conduct of the referendum.
Erdogan had a bumpy relationship with Trump's predecessor. Election board officials have said that they were trying to avoid suppressing votes and that the decision was not unprecedented in Turkey's elections.
Gunal also criticized announcements made by some Justice and Development Party leaders, saying: "The Turkish people have said their word and the Nationalist Movement Party has done what it should do". It also faulted Turkish authorities for holding the vote during a state of emergency, under which the government issued decrees that affected the outcome but could not be challenged.
Thousands of protestors took to the streets of Istanbul on Monday for a second night of protests against President Recep Tayyip Erdogan.
Turkish President Recep Tayyip Erdogan has rejected worldwide monitors" criticisms of Turkey's referendum, insisting the vote was the "most democratic election' seen in any Western country. Protesters claim that despite the win, there have been voting irregularities, such as the acceptance of ballots that did not bear official stamps, according to an Associated Press report.
Global monitors from the Organization for Security and Cooperation in Europe said the move undermined safeguards against fraud.