ISTANBUL - Turkey on Sunday removed 28 mayors accused of links to Kurdish militants or US-based cleric Fethullah Gulen, using emergency powers to replace them with state-appointed trustees in a move that sparked accusations of trampling on democracy.

The mayors have been suspended from their posts on suspicion of links to the Kurdistan Workers Party (PKK) which is waging a deadly insurgency in the southeast, or Gulen, who is blamed for the July 15 failed coup, an interior ministry statement said.

Using special powers under the state of emergency imposed in the wake of the abortive putsch, they have been replaced by state-appointed trustees, similar to administrators appointed to head a company that goes into bankruptcy.

Twenty-four of the outgoing mayors are accused of links to the PKK and four of links to Gulen, the ministry said. The reclusive cleric denies charges of masterminding the coup.

The move is the most important step yet taken by new Interior Minister Suleyman Soylu since he took over from Efkan Ala in a surprise reshuffle earlier this month.

Soylu said the move meant that local municipalities would no longer be controlled by "terrorists or those under instructions from Qandil", referring to the PKK's mountain base in northern Iraq.

The decree was issued under the three-month state of emergency imposed after the coup. The incumbents had been elected in 2014 local polls.

The municipalities affected - mainly in the Kurdish-dominated southeast - include hugely important urban areas known as centres of PKK activity such as Sur and Silvan in the Diyarbakir region and Nusaybin in the Mardin region.

The mayors of the cities of Batman and Hakkari in the southeast have also been replaced. The interior ministry said 12 of the mayors suspended were already under arrest.

Shortly after the move was announced, the authorities detained the former mayor of Cizre in Sirnak province, Leyla Imret, who in 2014 became one of Turkey's youngest ever mayors, the Dogan news agency said.

There were scuffles between protesters and police outside the town hall in Hakkari and also in Suruc in the Sanliurfa region where dozens were killed last year in an IS suicide bombing, Dogan said.

Meanwhile, security forces used water cannon to disperse a protest in Diyarbakir, an AFP correspondent said.

The US embassy in Ankara expressed concern over the clashes and emphasised the right to individual freedom of expression should be preserved.

"We hope that any appointment of trustees will be temporary and that local citizens will soon be permitted to choose new local officials in accordance with Turkish law," it said in a statement.

Critics have accused the government of using the state of emergency to impose a draconian crackdown that has eroded freedom of expression in Turkey.

Nobel-winning Turkish novelist Orhan Pamuk, writing in Italy's La Repubblica, expressed fear Turkey was "heading towards a regime of terror" after the detention of a prominent journalist on Saturday.

The government argues however that the emergency measures are essential with the country shaken by the coup and battling the PKK insurgency in the southeast.

The pro-Kurdish Peoples' Democratic Party (HDP), whose regional politicians were among the chief targets of the move, denounced the removal of the mayors as a "coup".

In a statement, it said the move was reminiscent of the military takeover of 1980 and "ignored the will of the voters".

It said the mayors in the mainly Kurdish cities had been elected on high turnouts and their dismissal would only amplify tensions in the region.

"The Kurdish problem will become even harder to solve... the people will not yield to this mentality," it said, calling on the government to stop "taking advantage" of the failed coup.

But Justice Minister Bekir Bozdag denied the authorities had ridden roughshod over democracy, accusing the suspended mayors of funnelling revenues to "terror" groups.

"Being elected does not grant a right to commit a crime," he wrote on Twitter.