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ISTANBUL, July 27 (Reuters) - Four leading members of the Turkish separatist Kurdistan Workers Party (PKK) were killed in an explosion at their camp in northern Iraq, Turkish private broadcaster CNN Turk reported on Friday.

The broadcaster said the explosion occurred in the Kandil mountains. No further details were immediately available.

Turkey has threatened to carry out a military incursion into neighbouring northern Iraq to crush thousands of PKK rebels they believe use the mountainous region as a base.

Ankara has raised troop levels in the restive southeast of Turkey to more than 200,000, with many near the Iraq border, senior security sources say, as part of a crackdown on rebels.

The AK Party government, which was reelected in a parliamentary election on Sunday, has resisted calls from the army to authorise a cross-border operation, while refusing to rule one out.

The United States, Turkey's NATO ally, has urged Ankara not to go into relatively stable northern Iraq.

Attacks on Turkish soldiers and civilians have escalated in recent months and a limited number of troops have crossed the border in so-called "hot pursuit" operations against rebels, according to security sources.

Officials in Kurdish-run northern Iraq have accused Turkey's army of shelling rebel targets inside the border.

The PKK launched its armed campaign for an ethnic homeland in southeast Turkey in 1984 and Ankara blames it for more than 30,000 deaths since then.

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