Six Turkish opposition parties reached consensus over the post-election regime

The new system would reverse changes made in a 2017 referendum that gave President Tayyip Erdogan near unchecked authority, Muharrem Erkek, a deputy head of the Republican People's Party (CHP), said.

"This (presidential) system has led to... arbitrary governance. We oppose this system which ... damages the basis of a democratic state of law," he said.

Erdogan has dominated politics for two decades with his Islamist-rooted AK Party, which has defended the presidential system, saying it streamlined a bloated state.

But an economic downturn has eroded support for the ruling bloc and saw the CHP, with support from other opposition parties, win over the two biggest cities in 2019 mayoral elections for the first time in about 25 years.

A poll published by Metropoll on Monday showed the AK Party and its nationalist MHP allies at 32.9% and 6.4% respectively - far below the 50% needed to obtain a majority in Turkey's 600-seat parliament. The next vote is scheduled for June 2023.

The opposition's "strengthened parliamentary system" would restore the post of prime minister and return the presidency to a largely ceremonial role, party officials said.

The changes would give parliament more authority over the budget and let any party with 3% or more of the vote get seats in parliament - cutting the current threshold from 10%, they added.

The parties said they would also overhaul the bodies in charge of appointing judges and prosecutors, overseeing elections and regulating media organisations.

The six opposition leaders met for the first time in Ankara earlier this month - widening an alliance that saw four parties join forces for the 2018 elections