A senior European Union source monitoring the situation said: "It looks like a relatively well orchestrated coup by a significant body of the military, not just a few colonels".
He said that the government remained in charge, and told NTV television by telephone: "It is correct that there was an attempt".
Later, army tanks were deployed at the entrance of Istanbul's Ataturk Airport.
The military's claim of control over the country was made in a statement carried by the Dogan News Agency and Turkish television broadcasts late on July 15.
"President Erdogan speaking to CNN-Turk on FaceTime", Katy Lee, a journalist for AFP tweeted. The report could not immediately be independently confirmed.
Prime Minister Binali Yildirim said the elected government remained in office.
But the sounds of explosions and continued to ring out in the capital. Private NTV television reported that one helicopter was shot down. "Our security forces have acted against these groups".
"We encourage U.S. citizens to shelter in place and do not go the U.S. Embassy or Consulates at this time", the embassy said. "Monitor local press for updates, avoid areas of conflict, and exercise caution if you are in the vicinity of any military or security forces". In particular, USA troops at Incirlik Air Base near the southern border with Syria and at Diyarbakir Air Base in the southeastern part of the country both have a direct role in the military campaign against the militants. It also learnt that the military coup was part of the Turkish army attempt to overthrow the government of President Erdogan.
The state-run Anadolu news agency said fighter jets under the control of loyalist forces were flying over the capital to strike at helicopters flown by coup supporters.
State-run Anadolu Agency is reporting that Chief of General Staff Hulusi Akar is being kept as a hostage, according to Hurriet Daily News.
U.S. Secretary of State John Kerry said he had called Foreign Minister Mevlut Cavusoglu to express his government's "absolute support for Turkey's democratically-elected, civilian government and democratic institutions". Social media including Twitter, Facebook and YouTube were suspended. In addition, sedia reports said ambulances were seen in front of the Turkey's military headquarters.
What's actually happening in Turkey remains unclear at this point, but tanks are out on some streets and flights from Istanbul's worldwide airport have been halted. "We pledge that good relations with all world countries will continue", the military said in the unnamed statement.
Critics also have blamed Erdogan for taking a hard line on Turkey's Kurdish rebels after the collapse of peace efforts, leading to deadly clashes that have increased military casualties.