One nation. One flag. One homeland. One state.

These eight words have been the key slogan of Turkish politics in the last years, strongly favoured by President Recep Tayyip Erdogan as a symbol of national unity.

But in the months before the July 15 failed military coup, there had been precious little such unity in Turkey with the southeast riven by conflict, the opposition in a constant war of words with the government and the country split down the middle over the polarising figure of Erdogan.

Yet as hundreds of thousands of Turks stood in solidarity against the coup in a sea of red at an Istanbul rally on Sunday attended by opposition leaders, it appeared some harmony had been found.

But it is unclear whether Erdogan will take this new unity forwards to heal the wounds in a deeply divided nation and keep his own confrontational instincts in check.

"The mood in the country is nervous, angry and dark, but also united with Erdogan," Soner Cagaptay, director of the Turkish Research Programme at The Washington Institute, told AFP.

"At this stage, Erdogan can play a unifier, which he has not done much in the past... or he can return to his divisive political platform."

Cagaptay said the current unity stemmed from the sheer historical significance of the night of July 15, which saw seized fighter jets bomb key targets in Ankara including parliament in a putsch attempt blamed on the US-based preacher Fethullah Gulen.

"The coup plot is probably the most traumatic political event in Turkey since the fall of the Ottoman Empire," he said, noting Ankara had not sustained such a serious military attack since it was occupied by the forces of the Turco-Mongol conquerer Timur in 1402.

Ozgur Unluhisarcikli, director of the German Marshall Fund's office in Ankara, said public fury over the plotters' actions had even rallied support behind the ensuing legal crackdown and state of emergency that has seen thousands detained.

"While many fear president Erdogan may use the coup attempt to further consolidate power and build an authoritarian regime, this fury has unified the populace in support of the measures," he said.

- 'Crush the PKK' -

As a symbol of the reconciliation, Erdogan is dropping legal suits for slander against opposition figures including Republican People's Party (CHP) leader Kemal Kilicdaroglu who had called him a "tinpot dictator" but spoke at the unity rally.

But while Erdogan invited Kilicdaroglu and Nationalist Movement Party (MHP) leader Devlet Bahceli to his presidential palace for talks that would have been unthinkable weeks ago, one man was conspicuous by his absence.

Selahattin Demirtas, co-chairman of the the Peoples' Democratic Party (HDP), the main political party of Turkey's largest ethnic minority the Kurds, was not invited to the palace or the big Istanbul rally.

While the HDP has more seats in parliament than the MHP and also unequivocally condemned the coup, the government accuses it of links to Kurdistan Workers' Party (PKK) rebels who are waging a deadly insurgency against the Turkish state.

After a two-and-a-half year ceasefire was shattered last year there appears no chance of a return to peace talks that had raised hopes of an end to the three decade conflict, with the government vowing to crush the PKK into submission.

"Erdogan will play a unified role, excluding the HDP and Kurdish nationalists. His attitude towards the HDP will only change after he has militarily defeated the PKK," said Cagaptay.

- 'Fragile unity' -

Meanwhile, Erdogan faces a huge challenge in keeping the country together in what will be a long haul in the next few years, with the president able to stay in power until 2024 and planning projects for his "New Turkey" ranging from high speed train lines to a Panama-style canal in Istanbul.

His most cherished political plan is agreeing constitutional changes to create a presidential system in Turkey that would enshrine greater powers in the head of state, a move that had seemed plagued with uncertainty before the coup.

The general secretary of the ruling Justice and Development Party (AKP) Abdulhamit Gul said Wednesday that talks would start this week with the opposition on a new constitution.

"This is a fragile unity and would be broken the moment president Erdogan tries to use it for his own personal goals," said Unluhisarcikli.