Suspected Kurdish militants shot and killed an official in Turkey's ruling AK Party late on Monday, authorities said, the second shooting of a politician in as many days in the strife-hit southeast.

Deryan Aktert, who headed the party's branch in Diyarbakir's Dicle district, was attacked in his office at 10:30 pm (1930 GMT) by suspected members of the Kurdistan Workers Party (PKK), the provincial governor's office said.

There was no immediate claim of responsibility, though the PKK - in a mounting conflict with government forces in the region bordering Iran, Iraq and Syria - often waits several days before making such announcements.

A day earlier, assailants killed Aydin Mustu, the ruling party's deputy leader in the Ozalp district of Van, a city 350 km (215 miles) to the east of Diyarbakir.

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 Islamic State there and in Iraq.

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

Suspected PKK militants set off a truck bomb, killing 15 people at a military checkpoint in Hakkari province on Sunday, officials said.

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 counter-terrorism investigation.

Ebubekir Bal, an AK Party parliamentarian representing Diyarbakir, said armed men had attacked Aktert's office last year.