Turkey's military said on Friday (July 15) it had seized power but President Tayyip Erdogan vowed that the attempted coup would be put down.

If successful, the overthrow of Erdogan, who has ruled Turkey since 2003, would be one of the biggest shifts in the Middle East in years, transforming one of the most important U.S. allies in the region while war rages on its border.

"We will overcome this," Erdogan said, speaking on a video call to a mobile phone held up to the camera by an announcer on the Turkish sister station of CNN. He called on his followers to take to the streets to defend his government and said the coup plotters would pay a heavy price.

An official said Erdogan was speaking from Marmaris on the Turkish coast where he was on holiday. Erdogan said he would swiftly return to Ankara.

Prime Minister Binali Yildirim said the elected government remained in office. However, it appeared that those behind the coup had the upper hand initially.

Airports were shut, access to Internet social media sites was cut off, and troops sealed off the two bridges over the Bosphorus in Istanbul, one of which was still lit up red, white and blue in solidarity with victims of the Bastille Day truck attack in France a day earlier.

Warplanes and helicopters roared over the capital Ankara. An explosion was heard in Ankara, where a helicopter opened fire.

Soldiers took control of TRT state television, which announced a countrywide curfew and martial law. An announcer read a statement on the orders of the military that accused the government of eroding the democratic and secular rule of law. The country would be run by a "peace council" that would ensure the safety of the population, the statement said.

TRT later went off the air.

The state-run Anadolu news agency said the chief of Turkey's military staff was among people taken "hostage" in the capital Ankara. CNN Turk also reported that hostages were being held at the military headquarters.