The Turkish prime minister has said the situation in the country is now largely under control after the military earlier said it had seized power.
Prime Minister Binali Yildirim's comments were reported by NTV television after a military attempt to bring down the government.
"We will overcome this," President Tayyip Erdogan said earlier, speaking by mobile phone to 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.
However, it appeared that those behind the coup had the upper hand initially.
Airports were shut, access to internet social media sites was restricted, 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.
The military and the government have been issuing conflicting statements since tonight's events began and many reports are yet to be confirmed.
A bomb tonight hit the Turkish parliament in Ankara, according to the state-run Anadolu agency.
Reuters witnesses in Istanbul reported the sound of a large blast, while broadcaster NTV said two people had been killed in clashes in the city.
Latest reports:
- Turkish F-16s shoot down helicopter carrying 'coup plotters': NTV television
- 17 police officers killed in an attack on their offices: State-run Anadolu agency reports
- Military opens fire on crowds in Istanbul, says AFP photographer
- Tanks open fire around Turkish parliament building
- Reports of gunfire heard at Istanbul airport
- Turkish military helicopters open fire at national intelligence agency HQ in Ankara
Warplanes and helicopters roared over the capital Ankara.
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 then went off the air, but has since resumed broadcasting.
A senior EU source monitoring the situation said it looked like a "relatively well orchestrated coup by a significant body of the military, not just a few colonels".
They added: "They've got control of the airports ... they control several strategic points in Istanbul.
"Given the scale of the operation, it is difficult to imagine they will stop short of prevailing. It's not just a few colonels," the EU source repeated.
Military 'seizes power' in Turkey; president calls on his followers to defend government https://t.co/IM1t7tR8BVhttps://t.co/v2noLZ5mqm
— RTÉ News (@rtenews) July 15, 2016
US urges support for elected Turkish government
US President Barack Obama has urged all parties in Turkey to back the "democratically-elected" government, after troops in the country launched a coup.
Detailing a call between Mr Obama and Secretary of State John Kerry, the White House said both agreed "all parties in Turkey should support the democratically-elected government of Turkey, show restraint, and avoid any violence or bloodshed".
Turkey's EU minister Omer Celik urged soldiers not to obey the orders of a faction in the military attempting to carry out a coup, according to broadcaster NTV.
"We will not hand over this democracy without giving our last breath," he added.
European Union foreign policy chief Federica Mogherini urged "restraint" in Turkey.
UN Secretary-General Ban Ki-moon appealed for calm as the world body sought to clarify the situation in Turkey.
The Kremlin said it was gravely concerned about tonight's events.
Kremlin spokesman Dmitry Peskov said events were moving too fast to fully understand what was happening.
However, he said Russia was concerned and wanted to see Turkey return to the path of stability and order, and for there to be a lawful outcome.
A group affiliated with US-based Turkish cleric Fethullah Gulen, who was accused by President Erdogan of being behind a coup attempt, has condemned the uprising. A US-based organisation close to Gulen has denied involvement.
The US State Department said Americans in Turkey should shelter indoors.
Other countries issued similar advice.
If successful, an overthrow of President Erdogan, who has ruled Turkey since 2003, would amount to one of the biggest shifts in power in the Middle East in years.
After serving as prime minister from 2003, Mr Erdogan was elected president in 2014 with plans to alter the constitution to give the previously ceremonial presidency far greater executive powers.
One European diplomat was dining with the Turkish ambassador to a European capital when guests were interrupted by the pinging of urgent news on their mobile phones.
"This is clearly not some tinpot little coup. The Turkish ambassador was clearly shocked and is taking it very seriously," the diplomat told Reuters as the dinner party broke up.
"However it looks in the morning, this will have massive implications for Turkey. This has not come out of nowhere."
In an statement sent by email and reported on TV channels, the military said it had taken power to protect the democratic order and to maintain human rights.
All of Turkey's existing foreign relations would be maintained and the rule of law would remain the priority, it said.
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.
Turkey is a NATO member with the second biggest military in the Western alliance.
It is one of the most important allies of the United States in the fight against so-called Islamic State, which seized swathes of neighbouring Syria and Iraq.
Turkey is one of the main backers of opponents of Syrian President Bashar al-Assad in that country's civil war, host to 2mi Syrian refugees and launch pad for the biggest influx of migrants to Europe since World War II.
Celebratory gunfire erupted in Syria's capital Damascus as word got out that Mr Erdogan had been toppled, and people took the streets to celebrate there and in the government-held section of the divided city of Aleppo.
The Irish Department of Foreign Affairs said it was aware of the situation.
We are aware of situation in Turkey. See updated travel advice here: https://t.co/z11g3pt4Bn. Call 01 408 2000 if you have any concerns
— IrishForeignMinistry (@dfatirl) July 15, 2016
