"I condemn, in the strongest terms, the attempted military coup in Turkey", Gulen said in a statement.
Bridges over the Bosphorus strait in Istanbul were blocked by troops late evening local time on Friday. Some strafed the headquarters of Turkish intelligence and parliament in the capital, Ankara, and others seized a major bridge in Istanbul.
Prime Minister Binali Yildrim said even though the death penalty is not in the constitution, legal changes would be considered.
Erdogan has cooperated with Washington in the fight against Islamic State, but relations have been rocky with US officials criticizing his increasing authoritarianism, Turkey's support for Islamist opposition groups fighting Syrian President Bashar al-Assad and the slow pace in sealing Turkey's border with Syria to foreign fighters. Events played out live over a range of connections, and dramatic if confused imagery through the hours of darkness eventually gave way at dawn to footage of soldiers crossing a bridge, arms raised in surrender - though to whom they were surrendering is unclear.
People surround a Turkish army tank in Ankara, Turkey July 16, 2016.
"Government should be won through a process of free and fair elections, not force", Gulen said. But Erdogan's government is blaming the chaos on the cleric, who lives in exile in Pennsylvania and promotes a philosophy that blends a mystical form of Islam with staunch advocacy of democracy, education, science and interfaith dialogue.
Gulen said democracy can not be achieved through military action.
Turkish media have suggested two men may have orchestrated the putsch: General Akin Ozturk, the former commander of the Turkish Air Force, and Lieutenant-General Metin Iyidil, a commander with the Land Forces Training and Doctrine Command.
On Saturday, Turkey's state-run news agency said the commander of the country's second army was arrested in connection with the coup. He criticized the President Tayyip Erdogan's government. The attempted coup appears to have its origins in the middle ranking officers rather than the high command, and there are reportedly over 100 arrests of "plotters" whom President Erdogan has promised to punish severely.
Why would they have done it?
It has had tensions with Mr Erdogan's AKP party over its political Islamism.
What has the response been outside Turkey?
"The President reiterated the United States' unwavering support for the democratically-elected, civilian Government of Turkey", the White House said.
The Nato military alliance, of which Turkey is a member, called for "full respect" for Turkey's democratic institutions.
Russian Federation said the situation was a threat to regional stability, while Iran said the events showed a "coup d'etat has no place" in the region.
Is it still safe to travel to Turkey?
The British Foreign Office advises that visitors stay indoors and avoid public places, especially where protests are occurring.
His conservative religious vision for Turkey's future has also alienated many ordinary citizens who accuse him of authoritarianism.
"My housemate, who is a Turkish Airlines cabin attendant, was held at the airport", he said. Domestic tension and suspicion, in turn, could undermine the consistency or effectiveness of Turkey's worldwide commitments and challenges, particularly when the military is involved.