Istanbul: Turkish President Recep Tayyip Erdogan has used the first anniversary of a coup attempt against his government to accuse an erstwhile ally of treason and portray civilian resistance to the plot as a triumph of the Muslim faithful.

Erdogan's fiery speech before a massive crowd in Istanbul highlighted the lingering trauma of the failed coup, which killed 250 people over the course of a terrifying night and day of violence. The speech also showed how the events have become an increasingly important political cudgel for the president and his supporters, with the victory over the coup plotters seen as a critical part of the government's popular mandate.

"Those traitors will always be remembered with hatred," Erdogan said, adding that Turkey "never hesitates to crush the heads of those who betray".

The speech on the Bosporus Bridge, which was renamed Martyrs Bridge last year and was one of the main battlegrounds of the 2016 coup, took place in front of thousands of people waving Turkish flags.

Erdogan also took part in late-night commemorations in the capital Ankara for those who died in the attempted coup, while opposition MPs boycotted the event.

The government has blamed the coup attempt on loyalists of Fethullah Gulen, a Turkish cleric who lives in exile in Pennsylvania. On that night, authorities said, renegade soldiers loyal to Gulen used tanks, planes and helicopters to occupy or attack television stations and public buildings, including parliament, and were defeated after Erdogan rallied citizens to the streets.

The events provided at least a momentary sense of unity in polarised Turkey: a shared shock and revulsion at the willingness of soldiers to crush people under tanks and strafe crowds from the air with heavy rounds.

That unity, though, has dissipated as the government cast a wide net in pursuit of its enemies, sweeping up the failed coup's alleged accomplices but also dissidents.

The still-murky timeline of the coup attempt and the staggering number of people caught up in the ensuing crackdown have fuelled the apprehension. About 150,000 people have been dismissed or suspended from their jobs, and 50,000 have been arrested. A state of emergency that gives the government extraordinary powers has remained in effect for almost a year, leading critics to charge that Erdogan seized on the coup attempt to bolster his power.

The president has argued that Turkey's unity persists and that the events of that night clarified the line between loyalty and sedition. The commemorative events on Saturday, planned in meticulous detail by the government, seemed designed to convey the sense of a national coming-together.

The country was blanketed by posters that depicted the scenes of the failed coup in the manner of epic paintings. Public transport and phone services were provided free of charge. Photo exhibits were set up in public squares, narrating the chilling sequence of events.

"Today is the day the country was saved," Ibrahim Agagul said as he looked at the pictures on Saturday outside an Istanbul municipal building where 20 people were killed. "Today, the people wrote a saga."

In his speech, Erdogan focused on the notion of shared sacrifice. "The treachery we face makes us stronger," he said, speaking at a bridge that was the scene of major clashes during the July 2016 violence.

His most pointed comments were a response to statements made earlier this year by Kemal Kilicdaroglu, the leader of the main opposition CHP, suggesting that the coup had unfolded with the government's knowledge.

Over the past few weeks, Kilicdaroglu led a  420-kilometre march that was an effort to highlight the purge by the authorities. Enis Berberoglu, one of the CHP's MPs, was jailed for 25 years, allegedly for spying.

The pro-Kurdish HDP has 11 MPs in jail and joined the march. It may be a sign that divisions within the opposition are narrowing, posing a greater threat to Erdogan's power.

"You should be ashamed of yourself," Erdogan said of Kilicdaroglu. "This nation is not a coward like you. This nation has a heart."

Washington Post, Reuters