A Kurdish militia allied with Turkey's rebel Kurdistan Workers' Party (PKK) imposed a curfew on the Syrian border town of Amuda on Friday after its forces shot three protesters dead, activists said.
The Kurdish Democratic Union Party (PYD), which has controlled large swathes of Hasakeh province in northeastern Syria since government troops withdrew from Kurdish-majority areas last year, said one of its fighters was killed in an ambush by a rival armed group.
Dozens of demonstrators were also injured when PYD fighters opened fire on Thursday on a protest against the militia's detention last week of a group of activists opposed to its grip on the town, the Britain-based Syrian Observatory for Human Rights said.
"At about 7:00 pm (1600 GMT) on Thursday, hundreds of residents of Amuda... gathered in the streets to demand the release" of three detainees from the PYD's prisons, said citizen journalist Havidar.
As protesters chanted anti-PYD slogans, "the Asaish (the PYD's security police) opened fire... on the protesters," Havidar said.
Amateur video distributed by activists showed fighters on a white pick-up truck firing live rounds, as cries were heard from the crowd.
The PYD said that its fighters had been ambushed by a rival armed group in Amuda, which lies on the border with Turkey.
"A PYD fighter has been killed at the hands of mercenaries from Amuda... Two others have been injured," the party said in a statement.
But independent Kurdish journalist and activist Massoud Akko said he did not believe anyone in the protest was armed.
"The protest was peaceful... There is no excuse for the use of weapons there," Akko told AFP via the Internet.
Amuda-based activist Neeshan Malle said that the PYD, the largest of the armed groups operating in Kurdish areas, had imposed a curfew on the town.
"No one is allowed on the streets, and there are snipers everywhere. All the shops are closed," Malle told AFP via the Internet.
Kurds form significant minorities in Iraq, Iran and Turkey as well as Syria.
In Syria, they make up around 15 percent of the population, living mainly in the northeast and in the Afrin area of the northwest.
Long marginalised by successive Arab nationalist regimes in Damascus, they have taken advantage of the uprising that broke out in March 2011 to assert their language and culture in Kurdish-majority areas.
The PYD champions a similar leftist, Kurdish nationalist platform to the PKK, the rebel group which struck a ceasefire deal with Ankara last month after fighting a bloody 29-year insurgency for self-rule in southeastern Turkey.