Turkey's overturning the election of a pro-Kurdish mayoral candidate triggered protests and clashes with police Tuesday, with opposition politicians rallying to reject the move.

Police used tear gas and water cannon to break up a demonstration in eastern city Van, where the DEM party said its candidate in Sunday's municipal elections was ruled ineligible at the last minute, while sympathisers also turned out in economic hub Istanbul.

The ruling was "unacceptable", Istanbul's re-elected mayor Ekrem Imamoglu, seen as a likely presidential challenger to incumbent Recep Tayyip Erdogan, posted on X (formerly Twitter).

He called on the government and electoral commission to "respect the people's will".

During nationwide municipal elections Sunday, DEM's Abdullah Zeydan had garnered over 55 percent of the vote in Van, which lies on Lake Van around 80 kilometres (50 miles) from Turkey's eastern border with Iran.

His exclusion left the way clear for the candidate from Erdogan's ruling Justice and Development Party (AKP) to the mayorship with just 27 percent of the vote, DEM added in a statement.

DEM said that just two days before the vote, the justice ministry had reversed a court decision that restored Zeydan's right to stand for election.

Zeydan had been elected to parliament on the HDP (now DEM) ticket in 2015 and arrested in 2016 with a dozen other deputies after criticising the Turkish army's aerial bombardments of outlawed Kurdish militants in the southeast.

 'Coup' 

 DEM co-chair Tuncer Bakirhan told reporters Van had suffered a "political coup", speaking to reporters during a rally outside the Supreme Election Board in the capital Ankara.

He added that the people of the region rejected mayors imposed by the exclusion of winning candidates.

DEM urged Erdogan's government, which was dealt a harsh nationwide blow in the elections, to "respect the will of the people" in Van.

Zeydan can appeal the decision that sparked protests in Van province, home to around 1.1 million people.

Television footage showed hundreds of protesters gathered outside DEM's Van headquarters in a show of solidarity.

"Abdullah Zeydan is our honour," they chanted. "Government-appointed trustees cannot deter us."

Police fired tear gas and water cannon to break up the protest.

Some 150 people also rallied on the Asian side of Istanbul to protest the regional electoral commission's decision, unfurling banners reading: "No to government trustees" and "Don't touch the will of Kurdish people", according to an AFP photographer on the scene.

 Pro-Kurdish sweep 

 AKP spokesman Omer Celik said the issue was at the discretion of the regional election commission, not the government in Ankara.

"If (the party) wants to appeal the decision, the mechanisms for that are clear," he told reporters after the party's central executive committee meeting.

Celik also criticised the scuffles between the police and protesters in Van, who he claimed hurled stones at the officers.

"Democratic protest is everyone's right. There is no place for turning it into a violent incident or attacking the police," he said.

Ozgur Ozel, leader of the opposition CHP Party whose candidates won Istanbul and Ankara as well as inner Anatolian cities in Sunday's vote, backed DEM, calling the overturning of Zeydan's victory a "disgrace".

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

Following the 2019 elections, fifty-two mayors elected in the southeast on the HDP (now DEM) ticket were stripped of office and replaced by state-appointed administrators for alleged ties to Kurdish militants.

That followed a 2016 coup attempt against Erdogan's government, which prompted a massive crackdown on opponents of all stripes -- even though the movement led by US-exiled cleric Fethullah Gulen was the main target.