ISTANBUL — Turkish opposition parties nominated candidates Friday to run against President Recep Tayyip Erdogan in next month's election, which will centralize even more powers in the hands of the president.

Last month, Erdogan called the election more than a year earlier than planned for June 24, and the opposition parties have been scrambling since to decide on their candidates.

Turkey's main opposition Republican People's Party, or CHP, nominated lawmaker Muharrem Ince for the presidency. Meanwhile, the pro-Kurdish Peoples' Democratic Party, or HDP, said its imprisoned former leader Selahattin Demirtas would be its candidate.

The election is hugely important as it will transform Turkey's governing system to an executive presidency, a constitutional change that was narrowly approved last year in a referendum. As part of the reforms, the office of the prime minister will be abolished, with its powers largely transferred to the president.

The successful candidate needs to secure more than 50 percent of the vote.

Speaking at a congress in Ankara, the 54-year-old Ince said he would not only represent his party's supporters but all of Turkey's 80 million citizens. Ince, who accused Erdogan of undermining Turkey's democracy, has been in parliament since 2002, representing his hometown of Yalova in the west of the country.

As a symbol for neutrality, the former physics teacher, who is known for his combative rhetoric, removed his CHP lapel pin to put on a Turkish flag pin.

"We will first establish justice. We will be impartial. We will be independent," Ince promised.

The CHP has been critical of Erdogan for his "one-man rule," scrapping the customary impartiality of the presidency.

Erdogan, meanwhile, told a crowd in Istanbul Friday that he had always promised to be a "different president" who would not shirk away from responsibility. He has been on the road for months shoring up support with multiple daily speeches.

The CHP has also slammed the government for committing a "civilian coup" through a massive crackdown following a failed 2016 coup attempt against the government.

More than 50,000 people were arrested and another 110,000 or so were dismissed from their public posts for alleged links to U.S.-based cleric Fethullah Gulen, who Erdogan accuses of masterminding the coup. Gulen denies involvement and the crackdown soon grew wider to include opposition lawmakers, journalists, activists and other dissenting voices. The government says the measures were necessary to combat terror.

Among those jailed is the HDP's candidate Demirtas, who was arrested in November 2016 pending trial on terror charges for alleged links to outlawed Kurdish militants. Eight other HDP lawmakers and nearly 4,700 HDP administrators and activist are imprisoned.

The HDP announced its nomination of Demirtas Friday simultaneously in Istanbul and Diyarbakir, the predominantly Kurdish southeastern province.

Demirtas accepted the nomination with a letter from his prison in western Turkey, saying he was a "political hostage." He called on supporters to "be my hand, my arm, my voice, my breath."

The former human rights lawyer ran against Erdogan in Turkey's first direct presidential election in 2014, garnering 9.7 percent of votes. He and his co-leader Figen Yuksekdag — also jailed — led the left-leaning party to parliament in two general elections during 2015.

It's unclear if Turkey's electoral board will approve Demirtas's candidacy. There have been no guilty verdicts in the numerous ongoing cases against him and he remains a parliamentarian, theoretically eligible to run.

Also in the running for the presidency is center-right Iyi Party leader Meral Aksener, a former interior minister who is considered a serious contender.