Turkey detained the mayor of the southeastern city of Van on Thursday, replacing him and two other mayors in the region, security sources said, pressing on with a crackdown on pro-Kurdish politicians.

The government appointed administrators to run the municipalities in Van and the provinces of Siirt and Mardin in the mainly Kurdish southeast, said the sources, who declined to be identified as they are not authorised to speak to media.

Turkey is fighting an insurgency by Kurdistan Workers Party (PKK) militants, but its arrest of many pro-Kurdish politicians and journalists in the crackdown has triggered concern among its Western allies about the human rights situation in the region.

State-run Anadolu Agency said police detained Van mayor Bekir Kaya at the council offices in the city on the shores of Lake Van, the heart of a province with a population of 1.1 million.

Police searched municipality offices and the houses of Kaya and four other council officials, Anadolu reported. Kaya was sentenced to 15 years in jail in January on a charge of "terror group membership", the agency said, but was appealing the verdict.

It said the interior ministry appointed Van Governor Ibrahim Tasyapan to run the municipality in place of Kaya, who is from the sister party of the pro-Kurdish Peoples' Democratic Party (HDP), parliament's second biggest opposition party.

Thousands of their members, including party leaders and dozens of mayors have been detained in investigations accusing them of PKK links.

The parties deny such ties and say they working for a peaceful resolution of the conflict.

At the start of November, Turkish authorities appointed an administrator to run the southeast's largest city of Diyarbakir, having arrested its co-mayors over alleged PKK ties.

On Wednesday, the mayors of Siirt and the eastern city of Tunceli were arrested over similar accusations.

The PKK is listed as a terrorist group by Turkey, the United States and European Union and launched an insurgency against the state in 1984 in which more than 40,000 people have been killed.

The crackdown on pro-Kurdish politicians has run parallel with a purge of people accused of ties to the U.S.-based cleric Fethullah Gulen, who is accused of orchestrating an attempted coup in July.

He denies the accusation.

More than 110,000 people have been sacked or suspended in the military, civil service, judiciary and elsewhere, while 36,000 people have been jailed pending trial as part of the investigation into the failed putsch on July 15.

In the latest purge, judicial authorities dismissed 203 judges and prosecutors over links to what Ankara terms the 'Gulenist Terror Group', Turkey's Official Gazette, which publishes state rulings, said on Thursday.

Human rights groups and some of Turkey's Western allies have voiced concern at the scope of the purges, fearing President Tayyip Erdogan is using the abortive military coup as a pretext to curtail dissent.