Dozens of riot police formed a cordon around the Information Centre of Kurdistan, an institute in central Paris with close links to the PKK where the bodies were found soon after midnight on Thursday. According to one Kurdish agency, workers broke in after seeing blood stains at the door.
Sakine Cansiz and two other women appeared to have been shot in the head, a French police source said. According to Kurdish media one woman had also been shot in the stomach.
It was not immediately clear who had carried out the killings; but the Kurdistan Workers Party (PKK) has seen internal feuding during an armed campaign in the mountainous Turkish southeast that has killed some 40,000 since 1984.
The killings came shortly after Turkey announced it had opened talks with Abdullah Ocalan, the PKK leader jailed on the prison island of Imrali, near Istanbul. The talks to end the conflict would almost certainly raise tensions within the movement over demands and terms of any ceasefire.
"Rest assured that French authorities are determined to get to the bottom of these unbearable acts," French Interior Minister Manuel Valls said at the scene, adding the killings were "surely an execution".
Any Turkish government contacts with the PKK, deemed a terrorist group by Ankara, Washington and the EU, are also highly controversial in the Turkish political establishment.
Last summer, preceding the move to talks, saw some of the worst bloodshed of the three-decades-old conflict.
Valls identified one of the victims as the head of the centre and said homicide and anti-terrorism units had been assigned to investigate the murders. A police source confirmed their nationality as Turkish.
"This is a political crime, there is no doubt about it," Remzi Kartal, a leader of the Kurdistan National Congress, an umbrella group of Kurdish organisations in Europe, told Reuters.
"Ocalan and the Turkish government have started a peace process, they want to engage in dialogue, but there are parties that are against resolving the Kurdish question and want to sabotage the peace process," he said.
An employee of the centre told French broadcaster that Cansiz was a founding member of the PKK, which is fighting for greater Kurdish autonomy in the Turkish southeast.
Many Turks fear such autonomy could stoke demands for an independent Kurdish homeland and undermine Turkey.
The Firat news agency, which is close to the group, said another victim was the Paris representative of the Brussels-based Kurdistan National Congress political group.
Firat said two of those killed were shot in the head and one in the stomach, and that the murder weapon was believed to have been fitted with a silencer.
"A couple of colleagues saw blood stains at the door. When they broke the door open and entered they saw the three women had been executed," French Kurdish Associations Federation Chairman Mehmet Ulker was reported as saying by Firat.
The government and PKK have agreed a framework for a peace plan, according to Turkish media reports, in talks which would have been unthinkable in Turkey only a few years ago. Ocalan is widely reviled by Turks who hold him responsible for a conflict that burns at the heart of the nation.
Turkish Prime Minister Tayyip Erdogan has introduced some reforms allowing Kurdish broadcasting and some concessions on language; but activists are demanding more freedom in education and administration.
The Kurdish question has taken on a particular urgency with the rise of Kurdish groups in neighbouring northern Iraq, where they control an autonomous zone, and in Syria. Turkey fears that Syrian President Bashar al-Assad could encourage Kurds to feed militancy in Turkey.
Turkish broadcasters reported police as saying the women had links to the PKK and could have been the victims of an internal feud.
A senior member of Turkey's ruling AK Party said internal feuds had occurred in the past whenever there were signs of progress towards peace.
"Whenever in Turkey we reach the stage of saying 'friend, give up this business, let the weapons be silent', whenever a determination emerges on this, such incidents happen," AK Party Deputy Chairman Huseyin Celik told reporters in Ankara.
"Is there one PKK? I'm not sure of that," he said.
Turkey's pro-Kurdish Peace and Democracy (BDP) opposition party, two of whose members were allowed to pay a rare visit last week to Ocalan on the island in the Marmara Sea where he has been jailed for the last 14 years, condemned the killings.
"We call on our people to hold protest meetings wherever they are to condemn this massacre and stand up for the Kurdish people's martyrs," the party's leaders said in a statement.
Among the crowd gathered behind police lines at the Paris institute were onlookers chanting slogans and waving yellow flags bearing Ocalan's likeness.