The four were killed in what newspapers said appeared to have been a settling of scores at a rear base of the PKK near Qandil, close to Iraq's border with Iran and Turkey.

A member of the PKK set off a belt packed with explosives during a meeting of PKK cadres, killing four of them and himself.

Riza Altun, one of the founders of the PKK and its chief financial operator, was said to be one of those present at the time of the explosion and his fate was not known, the dailies Hurriyet and Sabah said.

The PKK, which is regarded as a terrorist organisation by the European Union and Washington, has denied the reports in declarations made to the Europe-based pro-Kurdish news agency Firat.

Altun was placed under investigation in France in February for suspected terrorist activities and barred from leaving the Paris region.

He managed nevertheless to slip out the country to Austria where authorities allowed him to go on to northern Iraq despite an international warrant being out for his arrest.

Last week Turkish Foreign Minister Abdullah Gul lashed out at Austria for failing to extradite Altun, describing it as "a very big mistake" and saying it "erodes the foundations of the international struggle against terrorism."

The PKK has been fighting for self-rule in Turkey's mainly Kurdish southeast since 1984 in a conflict that has claimed more than 37,000 lives.

Rebels have stepped up their attacks this year, while Ankara has massed troops on the border with Iraq, fuelling speculation that it will launch a cross-border operation.

Ankara says it has grown weary of rebels enjoying a safe haven in northern Iraq, where they obtain weapons and explosives to launch attacks against Turkish targets across the border.

It has also accused the northern Iraqi Kurds of turning a blind eye to PKK presence on their territory and even supporting them.

Washington is opposed to any Turkish military action, fearing this could destabilise the relatively peaceful region and further strain tense relations between Ankara and the Iraqi Kurds, staunch US allies.