A local official from Turkey's ruling party has been shot and killed in the country's southeastern region, where Kurdish fighters affiliated with the outlawed Kurdistan Workers Party (PKK) operate, authorities have said.

Deryan Aktert, who headed the AK Party's branch in Diyarbakir's Dicle district, was attacked in his office on Monday night at 10:30pm local time (1930 GMT) by suspected PKK fighters, the provincial governor's office said on Tuesday.

There was no immediate claim of responsibility, but the PKK - in a mounting conflict with government forces in the region bordering Iran, Iraq and Syria - has been behind many of the attacks in the past.

Ebubekir Bal, an AK Party parliamentarian representing Diyarbakir, said armed men had previously attacked Aktert's office last year, according to Reuters news agency.

A day earlier, assailants killed Aydin Mustu, the ruling party's deputy leader in the Ozalp district of Van, a city 350km to the east of Diyarbakir.

Also in recent days, officials have blamed the PKK for bombings - both successful and failed attempts - throughout the country, including one just outside the country's capital on Saturday and another that killed 18 people on Sunday in Hakkari province.

Police in Diyarbakir said they had also detained 55 officials from the pro-Kurdish Peoples' Democratic Party (HDP) and its sister Democratic Regions Party (DBP) on Tuesday in a "counterterrorism" investigation.

A two-year ceasefire with the PKK collapsed in July last year, adding to the turmoil in a region already struggling with the civil war in Syria and the rise of the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS) there and in Iraq.

Since then, more than 600 Turkish security personnel and thousands of PKK fighters have been killed, according to the state-run Anadolu news agency.

The PKK, which launched its armed separatist rebellion in 1984, is designated as a "terrorist" organisation by Turkey, the United States and the European Union - a label it rejects.

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Source: News Agencies