The separatist PKK meanwhile warned that it would hold France responsible if the killers were not quickly found, as Ankara asked for increased security to safeguard its missions in France.

French judicial sources said the three female activists, including founding PKK member Sakine Cansiz, were each shot at least three times in the head, giving further credence to the theory of an execution-style hit.

Autopsies revealed that one of the women had been shot four times in the head and the other two shot three times, the sources said. A police source said that 7.65 mm bullets were found, indicating the use of automatic pistols.

The killings came days after Turkish media reported Turkey and the PKK leadership had agreed a roadmap to end the three-decade old insurgency that has claimed more than 45,000 lives.

The PKK, which took up arms in 1984 for Kurdish self-rule in southeastern Turkey, is considered a terrorist organisation by Ankara and much of the international community.

Experts have suggested a number of potential motives for the killings, including an attack by Turkish extremists and internal feuding within the PKK.

The three were found dead on Thursday at the Kurdistan Information Centre in the French capital's 10th district, after last being seen alive at the centre at midday on Wednesday.

Turkish Prime Minister Recep Tayyip Erdogan said the slayings bore the hallmarks of an internal feud, noting that the victims appeared to have given the killer or killers access to the centre.

"The place was protected not by one lock but many coded locks," Anatolia news agency quoted Erdogan as telling reporters. "Those three people opened it (the door). I do not assume they would open it to people they didn't know."

But the Turkish leader also upheld his earlier suggestion that the slayings could be aimed at derailing peace talks between Ankara and the PKK's jailed leader, Abdullah Ocalan.

"The killings could be the result of an internal feud or steps aimed at disrupting the steps we are taking with good intentions," Erdogan said.

Experts have said potential internal feuding could be linked to the peace process or to other PKK activities, in particular conflicts over money.

A French judicial source said police were currently running 21 investigations into potentially illegal fundraising by the PKK.

The group raises funds through a "revolutionary tax" on Kurdish expatriates that authorities in several countries have condemned as extortion.

The PKK's military wing, the People's Defence Forces (HPG), said in a statement on its website that France would be held to account if no progress is made in the investigation.

"France has a responsibility to immediately shed light on the massacre," it said. "Or it will be held responsible for the murder of our comrades."

About 1,000 Kurds on Friday marched to the building where the women were killed, shouting slogans such as "Turkey is a Terrorist", "Erdogan is a Murderer", and "We are All PKK".

Mourners left white and red roses outside the building and lit candles.

The PKK accused Ankara of trying to shift the blame on Kurds for what it called a "well-organised and professional political murder."

A Turkish diplomatic source meanwhile said Ankara had asked France to boost security at its missions.

There are around 150,000 Kurds in France, the vast majority of them of Turkish origin.