Turkish security forces killed 13 Kurdish militants in fighting in southeast Turkey overnight, security sources said, marking an escalation in violence at a time when cold winter weather normally limits clashes, Reuters reports.

Kurdistan Workers Party (PKK) fighters attacked some 10 different security force locations at 2:30 am in Cukurca in Hakkari province near the Iraqi border, the sources said.

One soldier and four militants were killed in the fighting and military operations were continuing in the area.

Separately, nine PKK guerrillas died in clashes with Turkish troops in a mountainous region of Bingol province after the soldiers discovered a winter shelter used by the militants.

Security sources said most of the militants were believed to have killed themselves by detonating hand grenades rather than being captured.

Three of the militants were capture alive, two of them wounded, the sources said.

More than 40,000 militants, soldiers and civilians have been killed since the PKK began its fight for self-rule in Turkey's mainly Kurdish southeast in 1984.

Turkey, the United States and the European Union all classify the PKK as a terrorist organization.