He has accused followers of his arch-enemy, US-based cleric Fethullah Gulen, of being behind the coup, which has led to a wave of some 50,000 arrests and sackings of suspected conspirators.
The state of emergency was needed “in order to remove swiftly all the elements of the terrorist organisation involved in the coup attempt,” Erdogan said at the presidential palace in Ankara.
Although the special measure vastly increases state security powers, Erdogan vowed there would be “no compromise on democracy”.
The announcement followed long meetings of Turkey’s national Security Council and cabinet chaired by Erdogan at the presidential palace.
A state of emergency gives the government extra powers to restrict freedom of movement, said an official, adding that it would not restrict financial or commercial activities as “international law sets limits of restrictions”.
Turkey in 2002 lifted its last state of emergency, which had been imposed in provinces in the south-east for the fight against Kurdish militants in 1987.
Article 120 of the constitution allows a state of emergency to be imposed “at a time of serious deterioration of public order because of acts of violence.”
Lesson in democracy
Global concern has grown as Turkish authorities have arrested or fired troops, police, judges, teachers and other civil servants in the aftermath of Friday’s failed bid to seize power by rebel troops.
Earlier the Turkish leader lashed out at critics of the sweeping purge, telling France’s Foreign Minister Jean-Marc Ayrault – who had warned Erdogan not to use the failed coup as a “blank cheque” to silence his opponents – to “mind his own business”.
“Does he have the authority to make these declarations about my person? No, he does not. If he wants a lesson in democracy, he can very easily get a lesson in democracy from us,” Erdogan said on al-Jazeera.
Earlier Wednesday US Secretary of State John Kerry, flanked by allied foreign ministers, said that while “we condemn this coup”, it was important that the response to it “fully respects that democracy that we are supporting”.
And German Chancellor Angela Merkel’s spokesman, in more direct comments, said that in Turkey “nearly every day we are seeing new measures that flout the rule of law and that disregard the principle of proportionality”.
Erdogan in the Al-Jazeera interview insisted that the arrests and suspensions had been carried out “within the law”, adding that “of course that does not mean we have come to the end of it”.