Thousands are expected to turn out for “national unity marches” in Istanbul and Ankara over the weekend, as Turkey commemorates one year since authorities quashed last summer's coup attempt.

Speeches will be delivered in the parliament and at the iconic Bosphorus Bridge, now called the July 15 Martyrs' Bridge, where President Recep Tayyip Erdogan will unveil the “Martyrs' Memorial” to remember those who died in the coup.

July 15 has been declared a national holiday. Public transportation in Istanbul and Ankara are free over the weekend, and bus destination signs were displaying messages of congratulations.

As in the night of the coup attempt, mosques across Turkey will simultaneously recite a verse, usually read before Friday prayers, to alert and invite Muslims to the streets.

Turkish soldiers attempted to overthrow the government and Erdogan using tanks, warplanes and helicopters on July 15 last year. The coup plotters declared their seizure of power on the state broadcaster, bombed the country's parliament and other key locations, and raided an Aegean resort where Erdogan had been holidaying.

But Erdogan had already left and the coup attempt was put down by civilians and security forces. Heeding a call by the president and ignoring a curfew announced by the coup plotters, thousands of people went out on the streets to resist the coup.

The Bosphorus Bridge was the scene of clashes between civilians and soldiers in tanks. Some 250 people were killed and more than 2,000 were injured across Turkey. Thirty-five coup plotters were also killed.

Turkey blames US-based cleric Fethullah Gulen for orchestrating the failed coup and has been demanding his extradition. Gulen denies the allegations.

In the aftermath of the coup attempt, Turkey declared a state of emergency that has been in place for a year, which has allowed the government to rule by decrees. More than 50,000 people have been arrested and some 100,000 public employees sacked for alleged links to Gulen and other terror groups.