The private Dogan news agency said that traffic police on the highway between the southeastern cities of Diyarbakir and Bitlis were attacked with rocket-propelled grenades and then rifles late yesterday.
As the clashes continued, another team of police deployed as reinforcements but their vehicle suffered an "accident" at the scene when it overturned, it added, without giving further details on the circumstances.
Dogan quoted Bitlis governor Orhan Ozturk as saying that five police were taken to hospital but three died of their wounds.
The PKK, which has been observing a ceasefire in its 30-year insurgency against the authorities in the southeast, is angry at Turkish policy on Syria as Islamic State (IS) militants advance on the Syrian Kurdish town of Ain al-Arab.
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Several Kurdish militant factions have warned of the risk of a resumption of violence if the government does not produce a convincing roadmap for the peace process by the end of the month.
The ruling Islamic-rooted Justice and Development Party (AKP) has insisted it remains committed to the peace process to end the violence, which has claimed 40,000 lives over the last three decades.
"Tearing this up or making threats is not going to get us anywhere and is just going to create problems. Let's sit down and talk," he added.