ANKARA (Reuters) - The presidential candidate for Turkey’s main opposition on Saturday called for the release of the pro-Kurdish opposition’s jailed candidate, challenging President Tayyip Erdogan to “let us race like men” in next month’s election.

Muharrem Ince, Turkey's main opposition Republican People's Party (CHP) candidate for the upcoming snap presidential election, greets supporters as he starts his campaign in Ankara, Turkey, May 4, 2018. REUTERS/Umit Bektas

On Friday, the Republican People’s Party (CHP) nominated Muharrem Ince to challenge Erdogan in the June 24 presidential election. The pro-Kurdish Peoples Democratic Party (HDP) nominated its jailed former leader Selahattin Demirtas.

“The HDP are also children of this nation, the AKP are also children of this country ... Don’t keep Demirtas in jail. Come, let’s race like men,” Ince told crowds of flag-waving supporters in his hometown of Yalova, where he held his first rally.

In his first interview with international media since being nominated, Demirtas, who has been in jail on security charges for a year and a half, told Reuters a fair election was impossible under the state of emergency imposed after the July 2016 coup attempt.

Erdogan last month called snap parliamentary and presidential elections for June 24, more than a year early, in order to switch to the powerful executive presidency narrowly approved in a referendum last April.

Ahead of the elections, Erdogan’s ruling AK Party (AKP) formed an election alliance, the “People Alliance”, with the Nationalist Movement Party (MHP), which supported Erdogan in the referendum.

Ince called on CHP members to sign for other candidates seeking 100,000 signatures in order to run for the presidency, including former interior minister Meral Aksener from the Iyi (Good) Party.

On Saturday, the CHP, Iyi Party, Saadet Party and Democrat Party signed a declaration marking a four-way election alliance called the “Nation Alliance”, pledging to remove polarization, instill independence for the judiciary and ensure basic rights and freedoms can be exercised.

Rights groups and Turkey’s Western allies have criticized Ankara for its deteriorating record on civil rights and have voiced concerns that the NATO member has been sliding further into authoritarianism under Erdogan.

Since the abortive putsch, authorities have carried out a sweeping crackdown on alleged supporters of the cleric Ankara blames for the coup attempt, detaining 160,000 people and dismissing nearly the same number of civil servants, the United Nations said in March.

The government says the measures are necessary due to the security threats it faces.