Hundreds of thousands of Turks protested in Istanbul on Saturday against the jailing of Mayor Ekrem Imamoglu, President Tayyip Erdogan's main rival, sustaining the largest demonstrations Turkey has seen in more than a decade.

A letter from Imamoglu was read out at the rally to cheers from the crowd. "I have no fear, you are behind me and by my side. I have no fear because the nation is united. The nation is united against the oppressor," the letter said.

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"They can put me in jail and try me as much as they want, the nation has shown that it will crush all traps and plots."

Hundreds of thousands of Turks nationwide have heeded opposition calls to protest since Imamoglu was detained last week and then jailed pending trial on graft charges.

Protests have been mostly peaceful but nearly 2,000 people have been detained.

The main opposition Republican People's Party (CHP), other opposition parties, rights groups and some Western powers have all said the case against Imamoglu is a politicised effort to eliminate a potential electoral threat to Erdogan.

The government denies any influence over the judiciary and says the courts are independent.

'JUSTICE WILL BE SERVED'

Hundreds of thousands of demonstrators waving Turkish flags and banners flocked to the sea-front rally at Maltepe on the Asian side of Istanbul for Saturday's "Freedom for Imamoglu" rally, organised by the CHP. Police imposed tight security around a venue where opposition supporters were gathering.

"If justice is silent, the people will speak," said one banner held aloft in the crowd.

"I am not afraid, and I will continue to resist. I call on everyone not to be afraid .... They fired me (from my job) but one day, justice will be served," said Gunay Yildiz, a former employee of Istanbul's Esenyurt district municipality.

Bunyamin Turan, a retired teacher, said: "When we look at the history of humanity, in all countries, all administrations, all regimes where there was such oppression, sooner or later, the people and those who resisted the oppression have won. The real owners of those countries won,"

CHP leader Ozgur Ozel, speaking at the rally, said millions of Turks were seeking Imamoglu's release and an election. He said the charges against the mayor were baseless and politically motivated, and the CHP called for a boycott of media outlets, brands and stores that it says are pro-Erdogan.

Last Sunday, the CHP held a primary election to endorse Imamoglu as candidate for the next presidential election. That is scheduled to be held in 2028, but the CHP is calling for an early vote, arguing that the government has lost legitimacy.

Interior Minister Ali Yerlikaya said this week that nearly 1,900 people had been detained since the protests began, adding that courts had jailed 260 of them pending trial as of Thursday.

Erdogan, who has dominated Turkish politics for over two decades, has dismissed the protests as a "show", warned of legal consequences, and called on the CHP to stop "provoking" Turks.

Since Imamoglu's detention, Turkish financial assets have plunged, prompting the central bank to use reserves to support the lira. The turmoil has sent shockwaves through the private sector.

The government has said the impact will be limited and temporary. The central bank said the economy's core dynamics were unharmed but it would take further measures if needed.