Three Kurdish women activists, including a co-founder of the Kurdistan Workers Party (PKK), have been killed overnight inside the Kurdish Information Centre in Paris, French police say.
Their bodies were found at around 2am on Thursday morning. All three were shot in the head.
"The scene leads one to think of an execution, but the investigation will determine the exact circumstances," a police source told the AFP news agency.
Manuel Valls, French interior minister, who visited the centre, also described the killings as an execution.
"This is a very grave matter and this explains my presence," he said at the scene. "This is unacceptable."
Al Jazeera's Rory Challands, reporting from Paris, said that Valls described the killings as "precise, assassination-style executions."
"Three bullet casings were found near the bodies, all of them with headshot wounds," he said.
Sources in Diyarbakir, eastern Turkey, told Al Jazeera that one of the women, Sakine Cansiz, was a co-founder of the PKK, the group involved in a decades-long armed campaign against the Turkish government.
Cansiz was one of the PKK's European representatives.
Al Jazeera's Goncha Chennai, reporting from the Turkish capital Ankara, said that Cansiz was an "important figure" in the PKK, especially in Europe.
Another victim was 32-year-old Fidan Dogan, who worked in the information centre, according to its director, Leon Edart.
The third was Leyla Soylemez, described as a "young activist".
"Soylemez was an activist from the National Congress of Kurdistan, the Brussels-based organisation," our correspondent said.
The three were last seen on Wednesday at the information centre, which was locked by late afternoon.
Andrew Finkel, a journalist and expert on Turkish politics, says the timing of the crimes is very significant.
It occurred shortly after the Turkish government resumed negotiations with Abdullah Ocalan, the jailed PKK leader, about disarming his group in exchange for greater rights for the country's Kurdish minority.
"There appears to be serious negotiations going on between Turkish government and the imprisoned leader or former leader of PKK," Finkel told Al Jazeera from Istanbul.
Hundreds of Kurdish protesters gathered outside the centre in Paris to protest the killings
"Now these talks appear to be going somehwere. I think if we needed confirmation that they are going somewhere is the fact that someone is trying to disrupt those talks.
"Many Kurds in Paris are blaming the [Turkish] government, but they do not really have a history of these rogue assassinations.
"It could be that there is an element within the Turkish state that is unhappy with the talks, but there is an equally probable explanation that its a faction within the PKK itself.
"Not everyone in the PKK is happy to see disarmament talks going ahead."
Zubeyir Aydar, a European representative for the PKK, blamed the attack on "dark forces" trying to interrupt the talks.
On the other hand, Huseyin Celik, deputy chairman of the Turkey's ruling AK Party, said the attack appeared to be the result of "an internal feud" within the PKK, and suggested there was an attempt to derail talks with the group.
Hundreds of Kurds gathered outside the information centre in Paris on Thursday to protest, with some chanting "We are all PKK!" and blaming Turkey for the killings.
"There was a demonstration of about 300-400 Kurds who came down to protest against the killings," Al Jazeera's Challands said.