Turkish riot police try to protect a person from a group of people of unknown affiliation who were attacking a rally of pro-Kurdish Peoples’ Democracy Party, (HDP) in eastern city of Erzurum, Turkey, Thursday, June 4, 2015. Several people were injured and a HDP election campaign car was set on fire by attackers. Turkey will hold general election on June 7, 2015 and approximately 56 million Turkish voters are eligible to cast their ballots to elect the 550 members of the Grand National Assembly.(AP Photo)

ANKARA, Turkey (AP) — Assailants fired on a campaign vehicle belonging to Turkey’s pro-Kurdish party and killed its driver, officials said Thursday, in the latest violence against politicians or political parties ahead of Sunday’s general election.

The governor’s office for Bingol province said the 35-year-old driver was found shot dead near the hired minibus of the People’s Democratic Party, or HDP, late Wednesday. It said an investigation had been launched.

The attack comes weeks after bomb explosions at two local HDP offices injured six people in southern Adana city and neighboring Mersin and days after officials said two supporters of a small Islamist party were killed in a fight with Kurdish party supporters in southeastern Turkey.

The motive for the latest attack was not known but the party is frequently accused by the ruling AKP party and by nationalists of links to Kurdish rebels fighting for autonomy in southeastern Turkey.

On Thursday, clashes broke out in the northeastern city of Erzurum between HDP supporters and people opposed to the party staging a rally there. The state-run Anadolu Agency said dozens of people were injured and a HDP election campaign car was set on fire.

The rally went ahead and the HDP blamed the clashes on President Recep Tayyip Erdogan and Prime Minister Ahmet Davutoglu who have been leading a fierce election campaign, often speaking out against the Kurdish party.

“If the prime minister and president target us, if they call us traitors who are trying to divide the country, then some people see it as their duty to attack us,” HDP leader Selahattin Demirtas told supporters in Erzurum.

The HDP, which has expanded its appeal beyond Turkey’s Kurdish regions and is attracting liberal and left-wing voters from the rest of Turkey, is playing a key role in the election. If the party reaches the threshold of 10 percent of total votes required to take seats in parliament, it could make it impossible for the ruling AKP to reach a supermajority in parliament. That would scuttle the AKP’s ambitions to introduce a new constitution to give executive powers to the president.

Meanwhile, the Anadolu Agency said an independent candidate reported missing four days ago was found alive on a highway in southern Gaziantep province. He had been kidnapped. His captors’ motive was not disclosed.

In other election-related violence last month in Adana, an AKP candidate was stabbed while electioneering and an opposition party candidate was shot in the knee.