The main opposition candidate in Turkey's presidential race called on Saturday for the release of a jailed Kurdish opposition candidate, challenging President Recep Tayyip Erdogan to "let us race like men" in next month's election.

Muharrem Ince was nominated by the opposition Republican People's Party (CHP) on Friday to contest the June presidential election. On the same day, the pro-Kurdish Peoples' Democratic Party (HDP) nominated its former leader, Selahattin Demirtas, who is in jail facing terror charges.

"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, said earlier on Saturday that a fair election was impossible in the current political climate.

"Demonstrations are banned, talking is banned, criticising the government is banned, even defending peace is considered terror propaganda," he said. "Hundreds of opposition journalists are arrested, dozens of TV and radio channels are closed.

"It is impossible for there to be fair elections in such an environment," Demirtas said in a hand-written response to questions submitted by Reuters News Agency to his lawyers.

Later on Saturday, four Turkish opposition parties announced they had formed a coalition to contest the legislative elections.

The main opposition CHP, the IYI (Good) Party, the conservative Saadet Party (SP) and the Democrat Party (DP) formed the Alliance for the Nation to stand against the People's Alliance of Erdogan's ruling AKP and the Nationalist Movement Party (MHP).

Three parties in the bloc, however, are fielding their own candidates for the presidential election.

Turks will go to the polls for parliamentary and presidential elections called by Erdogan for 24 June, more than a year earlier than scheduled.

Demirtas, the former leader of Turkey's second-largest opposition party, has been in jail for some 17 months on security charges and faces up to 142 years in prison if convicted.

A former human rights lawyer, Demirtas is one of Turkey's best-known politicians, winning votes beyond his core Kurdish constituency in 2015 elections.

Prosecutors charge that he and hundreds of other detained HDP members are tied to the militant Kurdistan Workers' Party (PKK). The HDP denies the charge.

#Demirtaş's message from Edirne prison to our candidacy launch event: There is no doubt it will be an unjust election campaign. But we won't lose heart. You must go from house to house and talk to them about how beautiful living equally, as sisters and brothers, will be. pic.twitter.com/dCkukR0gKk — HDP English (@HDPenglish) May 4, 2018

Turkish law bars anyone convicted of terrorism charges from running in elections, meaning Demirtas could be disqualified if convicted before the elections. "There is no legal obstacle to my candidacy because I am not convicted," the imprisoned leader said.

It would be a "scandal and a crime" if the courts blocked him by convicting him, he added.

Turkish media is saturated with coverage of Erdogan and his ministers - the president routinely speaks two or three times a day and the speeches are carried live by major broadcasters. Opposition parties get far less coverage, and the pro-Kurdish HDP almost none.

Meanwhile, more than 120 journalists have been detained and more than 180 media outlets have been closed since a state of emergency was introduced after a failed coup in 2016, rights group Amnesty International has said.

The HDP commands only about 10 to 12 percent support, but Demirtas is still likely to draw significant backing in a first-round presidential vote against Erdogan and other candidates, while also boosting the prospects of his party entering parliament.

'Political hostage'

Ince, who turned 54 on Friday, faces an uphill struggle to convince voters in the 24 June polls, facing Turkey's most experienced and rhetorically gifted campaigner in the shape of Erdogan.

Yet Ince's greatest political assets, his rhetorical skills and his impassioned speeches, have made him a favourite with the faithful of the CHP in recent years. Ince has often adopted a gloves-off approach towards Erdogan, raising the prospect of a fierce political campaign. He has famously vowed to sell off Erdogan's gigantic presidential palace, opened in 2014, should he be elected.

Demirtas' candidacy was announced by his party at rallies in Istanbul and the predominantly Kurdish city of Diyarbakir on Friday.

"The HDP's candidate is our Istanbul lawmaker, Selahattin Demirtas, who is being kept hostage," current party co-leader Pervin Buldan said in a broadcast that was streamed live on the internet.

"Selahattin Demirtas cannot carry out work ... or have the chance to meet with voters. This is why we demand that Mr Demirtas regains his freedom immediately," she said.

President Recep Tayyip Erdogan has said the elections will allow Turkey to move towards the powerful executive presidency which he has long advocated (AFP) The party released a letter from Demirtas on Friday, in which he called on supporters to help him during the campaign.

"As you may imagine, my hands are significantly tied here," he wrote. "Now, you, the youth, the women, are my hands, arms, voice and breath."

"Despite being held a political hostage in a cell, I believe I can fulfil this tough mission," he said, warning however that the campaign would be "hard and unjust".

Turkish authorities imposed a state of emergency after a failed military coup in July 2016 in which 250 people were killed. Since then, more than 160,000 people have been detained and nearly the same number of civil servants have been dismissed, the United Nations said in March.

Rights groups and some Western allies say Erdogan has used the putsch as an excuse to quash dissent. The HDP says as many as 5,000 of its members have been detained. On Saturday, it said co-leader Sezai Temelli had his passport confiscated at Istanbul airport on his way to Germany for election campaigning.

The government says the post-coup measures are necessary to confront the security challenges Turkey faces.

Turkey's opposition names senior MP as Erdogan poll challenger Read More »

When he called the snap 24 June vote last month, nearly 18 months earlier than scheduled, Erdogan said it would allow Turkey to move more swiftly to the powerful executive presidency which he has long advocated.

From prison, Demirtas wrote that Erdogan and his ruling AK Party, which has been in power for 15 years, called the early election over fears of waning support and said Kurdish voters would not vote for "a racist party".

"The AKP government is losing its support rapidly. The economy is also being dragged into a crisis. The government plans to control the state before hitting rock-bottom," he said. "The people in Turkey are fed up with the AKP and want to get rid of them, and the AKP surely knows this."