The Turkish military has released a statement saying armed forces have “fully seized control” of running the country.
A group within the military had earlier on Friday engaged in what appeared to be an attempted coup, Turkey’s prime minister said.
Binali Yildirim told NTV television: “It is correct that there was an attempt.”
Mr Yildirim did not provide details, but said Turkey would never allow any “initiative that would interrupt democracy”.
But the statement attributed to the military later said the takeover had been successful.
Earlier, military jets were heard flying over the capital, Ankara.
Media reports said ambulances were seen in front of Turkey’s military headquarters.
“We are focusing on the possibility of an attempt (coup),” Mr Yildirim had said.
“There was an illegal act by a group within the military that was acting out of the chain of military command.
“Our people should know that we will not allow any activity that would harm democracy.”
The Dogan news agency says one-way traffic on the Bosphorus and Fatih Sultan Mehmet bridges were blocked.
Video footage showed the bridge being blocked by military vehicles.
The Dogan agency reported that the statement said that the military did this “to reinstall the constitutional order, democracy, human rights and freedoms, to ensure that the rule of law once again reigns in the country, for the law and order to be reinstated”.
The military statement went on to say that “all international agreements and commitments will remain. We pledge that good relations with all world countries will continue”.
Al Jazeera news network has reported that Istanbul’s Ataturk international airport has been shut down.
“It seems there is dissent in the military ranks,” Al Jazeera’s Zeina Khodr, reporting from Gaziantep, said.
The two major bridges that have been shut down connect the Asian side of Istanbul to Europe.
Dogan News Agency footage showed cars and buses being diverted, according to Reuters.
Reuters witnesses in Istanbul, Turkey’s largest city, also spotted helicopters overhead.
In the capital Ankara, gunshots were heard, as military jets and helicopters were seen flying overhead, a Reuters witness said.
Turkey has had a history of coup attempts, the last time being carried out in 1997, which forced the resignation of then-prime minister Nemettin Erbakan.