The EU and Germany have urged Turkish leaders to heal bitter internal divisions after a contested referendum on handing the president greater powers.
The vote has major implications for the long-standing EU bid of Turkey, also a key NATO member.
Here are some of the main reactions:
"In view of the close referendum result and the far-reaching implications of the constitutional amendments, we... call on the Turkish authorities to seek the broadest possible national consensus in their implementation," said a statement issued by European Commission head Jean-Claude Juncker, EU foreign affairs chief Federica Mogherini and EU Enlargement Commissioner Johannes Hahn.
"The (German) government expects that the Turkish government will now seek respectful dialogue with all political and social forces in the country, after this tough election campaign," said Chancellor Angela Merkel in a joint statement with Foreign Minister Sigmar Gabriel.
Thorbjorn Jagland, secretary general of Europe's top rights watchdog, said Turkish leaders "should consider the next steps carefully ... in view of the close result."
It is of the utmost importance, said Jagland, "to secure the independence of the judiciary in line with the principle of rule of law enshrined in the European Convention on Human Rights."
Turkey is a full member of the Council of Europe, which "stands ready to support the country in this process", Jagland added.
According to Austrian Foreign Minister Sebastian Kurz, the referendum "shows how divided the country is". He added that "collaboration with the EU will be even more complex."
"Strange to see democracy restrict democracy. The majority has the right to decide, but I'm quite concerned about (the) new Turkish constitution," Danish Prime Minister Lars Lokke Rasmussen said on Twitter.
A NATO official said that the constitutional referendum in alliance member Turkey "is a matter for the Turkish people".