The DEM party's Abdullah Zeydan garnered more than 55 percent of the vote in Van in local elections on Sunday.

But the regional electoral commission claimed he was ineligible to stand due to a previous conviction and instead handed city hall to a candidate from President Recep Tayyip Erdogan's ruling Justice and Development Party (AKP), who managed only 27 percent.

"We made our objection to the Supreme Election Board cancelling the candidacy of our Van Greater City Mayor Abdullah Zeydan and giving the mandate to the AKP candidate," DEM said in a statement.

The party urged the election board "not to become complicit in this political coup".

The regional commission's decision followed the last-minute reversal of a court verdict that had restored Zeydan's right to stand for election.

Zeydan, who was elected as an MP on the HDP (now DEM) ticket in 2015, was arrested and jailed in 2016 after criticising the Turkish army's air campaign against outlawed Kurdish militants in the Kurdish-majority southeast.

He was released in 2022.

Violent protests against his ouster lasted through the night in Van province, which lies on Turkey's eastern border with Iran.

The local governor's office banned all demonstrations for two weeks after violent scuffles spread to several cities in the region, with some protesters setting police barricades on fire.

-'Double standards'-

Interior Minister Ali Yerlikaya said 89 people were detained, 26 of them in Van province, for joining unauthorised rallies and chanting slogans in praise of a "separatist terror organisation", referring to the Kurdistan Workers' Party (PKK) that has been blacklisted by Turkey and its Western allies.

In the southeastern Yuksekova district of Hakkari, 29 people were detained after violent clashes between protesters and police late on Tuesday.

Police again resorted to tear gas and water cannon to break up a protest in Van on Wednesday after visiting politicians made a statement of solidarity.

Istanbul's re-elected mayor Ekrem Imamoglu, seen as a likely presidential candidate in the 2028 election, called what happened in Van a "total aberration".

"We will be following this meaningless practice of double standards from Van to Hatay" in southern Turkey, Imamoglu told a crowd of around 500 supporters gathered outside Istanbul's main court after he was officially given a mandate to serve five more years.

His comments received applause from the crowd, who waved Turkish flags.

"This brother of yours will never give up on democracy, justice and law," he said, promising that he would not be a "bystander" in the face of injustice.

Imamoglu's CHP party, which made major gains in the local elections and maintained control of Istanbul and other big cities, has backed DEM in its battle against the Van ruling.

DEM -- accused by authorities of links to the PKK -- on Sunday claimed the mayorships of large towns in Turkey's Kurdish-majority southeast, including the region's largest city Diyarbakir.

The movement is also the third-largest party in Turkey's national parliament.