"At this moment of uncertainty in the country, the secretary-general appeals for calm, non-violence and restraint," said a statement issued by Ban's spokesman.

"Preservation of fundamental rights, including freedom of speech and assembly, remain of vital importance."

"The secretary-general is following closely and with concern the fast-moving developments in Turkey," said the statement, Xinhua reported.

"The secretary-general underscores that military interference in the affairs of any state is unacceptable," the statement said. "It will be crucial to quickly and peacefully affirm civilian rule and constitutional order in accordance with principles of democracy."

A military statement on Turkish media said Friday the armed forces have fully seized power in the country, but Turkish President Recep Tayyip Erdogan said early Saturday the coup attempt has failed, urging people to protect democracy.