DIYARBAKIR, Turkey (Reuters) - Kurdish militants attacked military outposts in southeast Turkey overnight, killing three Turkish soldiers, security sources said on Wednesday.

Armed with mortars and rifles, the Kurdistan Workers Party (PKK) guerrillas launched the raids at Cukurca in Hakkari province, a mountainous area bordering Iraq and Iran, the sources said.

They said the Turkish military were searching for the militants in the Turkey-Iraq border region.

The PKK - designated a terrorist group by Turkey, the United States and European Union - has carried out a steady stream of attacks on military targets in recent months, stepping up a 28-year-old insurgency.

More than 40,000 people have been killed in the conflict since the PKK took up arms in 1984 with the aim of carving out a Kurdish state.

Fighting between the army and the PKK intensified over the summer, a development which Ankara sees as linked to the chaos in neighboring Syria. Prime Minister Tayyip Erdogan has accused Syria's President Bashar al-Assad of arming the PKK militants.

(Reporting by Seyhmus Cakan; Writing by Seda Sezer; Editing by Louise Ireland)