The bodies of Sakine Cansiz, who promoted the role of women in the armed Kurdistan Workers Party (PKK) group, and the two other women were found soon after midnight on Thursday (local time) in an institute in central Paris with close links to the PKK.
They appeared to have been shot in the head, a French police source said. Kurdish media said one woman was also shot in the stomach. Workers had broken in to the room in the Information Centre of Kurdistan after seeing blood stains at the door.
Cansiz had been a prominent figure in the PKK before falling out with the group's factionalised leadership. A 1995 photograph shows her standing next to militant leader Abdullah Ocalan, wearing olive battle fatigues and clutching an assault rifle.
It was not immediately clear who had carried out the killings; but the PKK has seen intermittent internal feuding during an armed campaign in the mountainous Turkish southeast that has killed some 40,000 since 1984.
Turkish nationalist militants have in the past also been accused of 'extra-judicial killings' of Kurdish activists but such incidents have been confined to Turkey.
Among the crowd gathered behind police lines at the Paris institute were onlookers chanting slogans and waving yellow flags bearing Ocalan's likeness.
Turkish Prime Minister Tayyip Erdogan said it was too early to apportion blame.
"This may be an internal reckoning. Aside from this, we are engaged in a struggle against terrorism ... but there are people who don't want this. This could be a provocative undertaking by these people," he said during a visit to Senegal.
The killings came shortly after Turkey announced it had re-opened talks with 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".
France is home to a large number of Kurds, many of them having emigrated in the 1960s and 1970s, but there is also a number of Kurdish pro-PKK exiles such as Cansiz. Other Kurdish activists have settled in Germany and Sweden.
Any Turkish government contacts with the PKK, deemed a terrorist group by Ankara, Washington and the EU, are highly controversial in the Turkish political establishment.
Last summer, the months preceding the move to talks, saw some of the worst bloodshed of the three-decades-old conflict. Television footage of soldiers' coffins returning home draped in the red Turkish flag inflamed nationalist tensions.
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.
The two other victims were named as Fidan Dogan, 28, and Leyla Soylemez, 25.
"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.
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.
Many Turks fear such autonomy the PKK is seeking could stoke demands for an independent Kurdish homeland, in Turkey and beyond Turkish frontiers, 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. It said 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.
Female militants have played a significant role in the PKK's insurgency, partly reflecting a principle of equality within the group's Marxist ideology. In some cases, desire to avenge the killing of other family members was the motivation for joining, for others it was a way out of family repression, analysts say.
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.
Turkish broadcasters reported police as saying the women retained links to the PKK and may have been victims of an internal feud.
Several members of the Kurdish community in Paris said that Cansiz, who was in her fifties, was an emblematic figure who had been imprisoned in Turkey before obtaining asylum in France.
"She was in charge of communicating information on events in Turkey, she would denounce arbitrary arrests, unsolved murders" of Kurds in Turkey, said a member of the Arts and Culture Academy of Kurdistan who asked not to be identified.
Turkish political analyst Emre Uslu, who previously worked in Turkey's counter-terrorism police unit, said in a blog that the killing of Cansiz could point to a split within the PKK.
He said Cansiz was a leading member of a faction within the PKK that had in the past opposed Ocalan's moves towards peace.
"This group ... could at any moment sabotage the peace talks which will be held with the PKK," Uslu said. "For Turkey to sit down with the PKK before its internal problems are solved is considerably problematic."
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.