Eleven civilians were killed when a Syrian warplane bombed a Kurdish village in the oil-producing province of Hasaka in northeastern Syria on Sunday, Kurdish activists said.
The raid, which killed mostly women and children, is the biggest loss of Kurdish life from loyalist attacks since the start of the two-year uprising against President Bashar al-Assad, they said.
The circumstances of the attack on the impoverished village of Haddad, 60 km (40 miles) northeast of the city of Qamishli, are not clear, but it appears that a rebel force specialising in raiding oil wells had deployed on a hill near the village, the Kurdish sources said.
A statement by the Kurdish National Council said the attack was a "serious escalation by the regime" following a series of raids on rural areas near Qamishli, where fighting between rebel brigades and President Bashar al-Assad's military has intensified in the last week.
The Kurdish National Council is an umbrella grouping of the main Kurdish parties in Syria, excluding the Syrian branch of the militant Kurdistan Workers Party (PKK), which effectively has allied with Assad.
With his forces overstretched, Assad has sought to keep Hasaka from joining the revolt by handing the PKK control over parts of the province.
Distrust between Syria's Sunni Arab majority and the country's Kurds, who are also Sunni, have been deepening during the two-year, Arab Sunni led uprising against Assad, with Arab figures in the opposition suspicious that the Kurds may carve out an autonomous province in the east, and Kurdish politicians accusing the opposition of disregarding Kurdish rights and seeking to secure the oil-producing northeast, which accounts for a large proportion of Syria's oil production.
Oil output stood before the revolt at a modest 300,000 barrels per day.
In January this year the PKK fought hardline Islamist rebel fighters in the Syrian town of Ras al-Ain on the border with Turkey. But the situation eased after the intervention of senior opposition figures. The rebels however have resumed attacks on army positions in areas of the Qamishli countryside in recent weeks.
In 2004 Assad put down an uprising by Syria's Kurds, who comprise an estimated 10 percent of the population. But the community, wary of the rise of militant Islamists in the revolt, have not joined the armed movement against Assad.
Assad's newfound support for the PKK, after years of persecuting the group, has also caused fissures in the Kurdish community.