Many thousands of Turks massed Sunday for the first cross-party rally to condemn the coup attempt against President Recep Tayyip Erdogan, amid a purge of suspected state enemies.

Istanbul's Taksim square was transformed into a red sea of national flags as Erdogan's ruling Islamic-conservatives and the opposition secular camps briefly set aside their differences in a show of national unity.

But in stark contrast to the broadly celebratory mood in Istanbul, human rights group Amnesty International in London claimed it had "credible evidence" of the beating and torture of post-coup detainees.

The official number of those in custody since the July 15 putsch has surged above 13,000 soldiers, police, justice officials and civilians in a wave of arrests that has alarmed NATO allies and European leaders.

Despite the high tensions since the coup attempt, the mood at the Istanbul rally was strongly patriotic.

"We defend the republic and democracy" read one sign in the vast crowd, while others declared "Sovereignty belongs to the people alone" and "No to the coup, yes to democracy!"

- 'Turkey stood proudly' -

A few banners also protested the post-coup state of emergency, with one proclaiming "No to the coup, no to dictatorship".

The mass event was called by the biggest opposition group, the secular and centre-left Republican People's Party (CHP), many of whose members carried pictures of modern Turkey's founding father Mustafa Kemal Ataturk.

Its leader Kemal Kilicdaroglu told the crowd that, amid all the turmoil, "the parliament stood proudly, Turkey stood proudly, lawmakers stood proudly, people in this square have stood proudly, and democracy won!"

But he also stressed that now "the state should not be governed by anger and revenge".

"The culprits of the putsch should be tried lawfully," he said, warning that torture and ill-treatment would put the state on par with the putschists.

In London, Amnesty charged that the government was already using such methods, citing interviews conducted with lawyers, doctors and one person on duty in a detention facility.

Amnesty claimed it had "credible evidence" some detainees were being "subjected to beatings and torture, including rape, in official and unofficial detention centres in the country".

The group said it had received reports that detainees were being denied food, water and medical treatment and being held in "stress positions" for up to 48 hours.

"Turkey is understandably concerned with public security at the moment, but no circumstances can ever justify torture and other ill-treatment or arbitrary detention," said Amnesty's Europe director John Dalhuisen.

He urged the Turkish authorities to stop "these abhorrent practices" and allow international monitors into detention centres.

- 'In cold blood' -

In Ankara, a senior official denied Amnesty's claims, saying: "The idea that Turkey, a country seeking European Union membership, would not respect the law is absurd".

"We categorically deny the allegations and encourage advocacy groups to provide an unbiased account of the legal steps that are being taken against people who murdered nearly 250 civilians in cold blood."

Turkey has undergone a seismic shift since the night of violence when renegade soldiers sought to topple Erdogan but were stopped by crowds of civilians and loyalist security forces.

In the latest reaction, Yildirim said Turkey would disband Erdogan's 2,500-strong Presidential Guard, almost 300 of whose members have been detained. Under new emergency powers, they can be held without charge for 30 days.

Erdogan's government has also sacked thousands of teachers, professors and civil servants and closed schools and universities.

Also detained in the sweep was Halis Hanci, an alleged senior aide to US-based cleric Fethullah Gulen -- the reclusive spiritual leader whom Turkey accuses of having orchestrated the plot to overthrow Erdogan.

The preacher, who lives in a compound in rural Pennsylvania and whose foundation runs a global network of schools, charities and media interests, has strongly denied the accusations against him.

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