(Adds PKK deaths, soldiers hurt, paragraph 8)

DIYARBAKIR, Turkey, June 18 (Reuters) - Turkish state prosecutors opened an investigation on Monday into Masoud Barzani, head of the autonomous Kurdish region of northern Iraq, whom Ankara suspects of supporting Turkish Kurdish rebels.

The probe coincides with a buildup of Turkish troops and tanks in mainly Kurdish southeast Turkey amid speculation that they may stage a major incursion into northern Iraq to hit bases of the banned Kurdistan Workers Party (PKK) located there.

A Turkish nationalist organisation asked prosecutors in Diyarbakir, the largest city of Turkey's southeast, to open the probe into the accusations over the PKK, and called for the seizure of any assets, including property and bank accounts, that Barzani may own in Turkey.

Barzani once had good ties with Ankara, but these have deteriorated sharply in recent months after he used harsh language to criticise Turkey's approach to Iraq's Kurds and said there could be no question of his forces tackling the PKK.

Ankara is anxious to prevent the emergence of an Iraqi Kurdish state in northern Iraq, fearing this could fan separatism among its own large Kurdish population in southeast Turkey and also destabilise the broader region.

Turkey, which faces elections next month, says it has the right under international law to send troops into Iraq to crush the PKK if U.S. and Iraqi forces fail to act.

Ankara blames the PKK for the deaths of more than 30,000 people since the group launched its armed campaign for an ethnic homeland in southeast Turkey in 1984.

On Monday, three PKK members were killed in a firefight with Turkish troops in Siirt province in southeast Turkey. Separately, three Turkish soldiers were hurt when their vehicle hit a landmine in nearby Tunceli province.

PKK attacks on civilian and security targets in Turkey have increased over the past few months, putting more pressure on Prime Minister Tayyip Erdogan to get tough with the rebels.

Turkish media said on Monday Iraqi Prime Minister Nuri al-Maliki would visit Ankara this month at Erdogan's request to discuss the security situation in northern Iraq.

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