DIYARBAKIR: An explosion in a police compound in Turkey’s southeastern city of Diyarbakir killed one person and wounded several others on Tuesday, days ahead of a national referendum, but the interior minister appeared to rule out foul play.

The blast, which caused part of the police compound’s roof to collapse, occurred during the repair of an armored vehicle, the Diyarbakir governor’s office said. It said one person had died in hospital and the cause of the blast was unknown.

But Interior Minister Suleyman Soylu said the explosion, which sent a large plume of smoke over surrounding buildings and left a crater in the ground, appeared to have been an accident.

“The blast was in a part of the building for riot police, where maintenance is carried out on vehicles,” he was quoted by broadcaster CNN Turk as saying during a speech in Istanbul.

“At the moment, it seems there is no outside interference, and the explosion came from the vehicle under repair. One person is trapped under the wreckage,” he said.

Ambulances, police and rescue teams were rushed to the scene in the city’s Baglar district, where thick smoke was seen rising into the air.

The explosion came ahead of a hotly contested referendum on Sunday on broadening President Recep Tayyip Erdogan’s powers, a constitutional change opposed by many in Turkey’s predominantly Kurdish southeast.

The blast was in the central, largely residential district of Baglar, where a car bombing by suspected Kurdistan Workers’ Party (PKK) militants wounded scores of people last November. The outlawed PKK has been designated by Ankara, the US and the EU as a terror group.

Diyarbakir and its region has over the last year been repeatedly hit by PKK attacks targeting the security forces. The militants have fought an insurgency mainly in the southeast region including Diyarbakir for more than three decades to press demands for Kurdish autonomy. Violence has flared since a cease-fire collapsed in July 2015.

Turks will on Sunday vote on whether to approve constitutional changes giving Erdogan executive presidential powers, which critics say would drag the country into one-man rule.