The outcome of Turkey's elections on Sunday could depend on a jailed presidential candidate's sway over voters more than 1,200 km (750 miles) away in the country's largely Kurdish southeast.

In prison since 2016 and now on trial on terrorism-related charges, Selahattin Demirtas is the driving force behind the pro-Kurdish Peoples' Democratic Party (HDP) bid to win the 10 percent of votes that parties need to enter parliament.

With virtually no media coverage of him or his party, Demirtas has got his message out through social media, party colleagues and his wife Basak, who regularly visits him in Edirne Prison near the northwest border with Greece and Bulgaria.

While he has no formal role leading the party from jail, there is no legal obstacle to him running for president.

"They think they cut him off from the outside world but they can't see the thousands of Demirtases here," HDP co-leader Pervin Buldan told a cheering crowd waving green, white and purple party flags in the southeastern town of Silvan.

Demirtas appeared for the first time on television in 20 months on Sunday night when he made a scheduled 10-minute election address allotted to all candidates on state TV. Thousands cheered and applauded as they watched the speech on giant screens at an HDP rally in Istanbul.

President Tayyip Erdogan dubs Demirtas "the terrorist in Edirne" and his party an extension of the Kurdistan Workers Party (PKK) militant group. Demirtas and the HDP deny links to the PKK.

"They tried to come between us with the terror group by turning you against each other on the streets with threats, looting and extortion," Erdogan told a rally in Diyarbakir, the largest city in the southeast.

Several recent polls have suggested Erdogan's ruling AK Party could lose its parliamentary majority on June 24, which would put a brake on his ability to exercise the powers of the new executive presidency.

Polls on average put support for the HDP around 10 percent nationwide.

If the HDP fails to make the cut-off, dozens of seats will go to the AK Party, the second most popular in the region, which would almost certainly guarantee a parliamentary majority.

HDP voters could also be influential in determining whether Erdogan wins the presidential vote, which requires a simple majority and which polls suggest could go to a second round.

KURDISH PROBLEM

More than 40,000 people have been killed in the conflict with the PKK, designated a terrorist group by Turkey, the United States and European Union. After a 2-1/2 year peace process collapsed in 2015, the southeast suffered through some of the most intense conflict since the insurgency began in 1984.

Erdogan says the government's hardline response has made the region the most peaceful it has been for 40 years. He said in Diyarbakir the AKP had solved the Kurdish problem, citing reforms in areas of cultural rights, education and language.

Such comments are fiercely rejected in Silvan, 80 km (50 miles) east in a farming area, where the HDP won 88 and 89 percent of the vote in two elections in 2015.

This week's election is being held under emergency rule, imposed across Turkey after a 2016 attempted coup, which gives the government sweeping powers to impose tight security.

"Look at the pressure these elections are being held under," said farmer Emre Binen, 36, pointing to police searching those arriving at the HDP rally and armed police monitoring the crowd from a building above the square.

The HDP's campaigning abilities have been hit by a crackdown which led to 11 of its MPs losing parliamentary status and a similar number jailed on terrorism charges. The state seized control of dozens of municipalities from an HDP affiliate party, arresting mayors and thousands of party members.

The crackdown was conducted in tandem with a nationwide purge of tens of thousands of people over alleged links to an Islamic cleric accused of orchestrating the failed 2016 putsch.

Polling stations have been relocated in some southeast areas, which officials say is meant to prevent PKK intimidation but the HDP says aims to curb its votes.

HDP supporters argue the moves have fuelled sympathy for their cause. Demirtas' wife Basak said jailing her husband, who could be sentenced to up to 142 years in prison, had only increased his appeal.

A video of Basak Demirtas speaking to her husband by phone as her family sat around her has been viewed on his Twitter account 1.35 million times.

"Selahattin being inside did not lessen the people's love for him. On the contrary it increased it," she told Reuters TV before one of her weekly prison visits.

To make it to parliament as it did in 2015, however, the HDP will have to win over leftist and liberal voters in western Turkey in addition to its core Kurdish southeast support. Kurds make up around 20 percent of Turkey’s 81 million people.

SOCIAL TRAUMA

The HDP won 73 percent and the AKP 21 percent of the Diyarbakir vote in the last election in November 2015. Soon after, fighting between security forces and militants devastated much of its ancient Sur district.

Such conflict has directly affected current candidates.

HDP's Remziye Tosun was a Sur resident whose house was among thousands destroyed in the urban warfare. She was picked to run for office after a spell in jail, with her baby, accused of aiding militants.

AKP candidate Oya Eronat, also from Sur, entered politics a decade ago after her teenage son was killed when a car bomb planted by the PKK exploded in front of a tutoring centre.

Speaking in Diyarbakir, she said security forces had brought calm and "the most peaceful election so far", without the PKK intimidation which she said the AKP suffered in the past.

Eronat's views were echoed by AKP voters who said HDP supporters wilfully ignored reforms and stability under Erdogan's rule out of loyalty to the Kurdish cause.

"I am Kurdish and have no problem with the state. I can talk in Kurdish and listen to Kurdish songs. You couldn't do that before Erdogan. It was too dangerous to go into the streets," said company manager Murat Tasdemir, 42, in a shopping mall.

Diyarbakir's appearance has been transformed in recent years by such malls, highways and apartment blocks. But the region is poorer than western Turkey, and HDP candidate Selcuk Mizrakli said below the surface there was social trauma.

Mizrakli, facing up to 23 years in jail on terrorism-related charges, operated on hundreds of civilians and police officers wounded in the region's conflict as a surgeon - an experience which drove him into politics.

"The people we speak to on the streets voice anger, a feeling of being wounded and victimized," he said. "But there is also patience, determination and belief that if we stand together we can change things.