An air strike killed at least 12 people and wounded more than 30 in the northeastern Syrian town of Ras al-Ain todau, the Syrian Observatory for Human Rights said, AFP has reported.
Among the dead were four civilians and eight rebels, the Britain-based watchdog said.
"The warplane hit the Mahata district in the southwestern part of the town. This area is controlled by the (jihadist) Al-Nusra Front, Ghuraba al-Sham and other rebel battalions," the Observatory's Rami Abdel Rahman told AFP by phone.
The northeastern sector of the town, located in the mainly Kurdish province of Hasakeh, is controlled by Kurdish militants, he noted.
"A MIG aircraft made two consecutive bombing raids around 10:15 am (0815 GMT)," a Ras al-Ain activist who identified himself as Hevidar told AFP over the Internet.
"These led to the death of nine civilians, including a child, not more than eight years old... and many of the wounded civilians were transported to hospitals in Turkey," said Hevidar.
Many people who had recently returned to the town after being displaced during previous violence were forced to flee once again across the border, he added.
In unverified video footage posted on the Internet by activists, a group of men wearing coats are seen lifting pulling bloodied and limp bodies from beneath a pile of steel and other collapsed building materials.
A fire can be seen blazing in the background as the men load the bodies into the back of a truck.
Ras al-Ain was the scene of fierce clashes between fighters loyal to the Kurdish Democratic Union Party (PYD) -- which has close ties to Turkey's outlawed Kurdistan Workers' Party (PKK) -- and the Al-Nusra Front and Ghuraba al-Sham in late November.
The Observatory, which relies on a network of activists, lawyers and medics, later reported that clashes had died down after the two parties managed to strike an agreement.Turkey scrambles jets as Syrian gov't forces bomb border town
Turkey scrambled fighter jets along its border with Syria on Monday after Syrian government forces bombed rebel positions in the frontier town of Ras al-Ain and stray shells flew into Turkish territory Turkish security sources said, Reuters has reported earlier today.
Rebels overran Ras al-Ain almost a month ago in fighting which has triggered some of the biggest refugee movements of Syria's 20-month civil war, and has tested Turkey's resolve to defend itself against any spillover of violence.
The security sources said Turkish F-16 jets were scrambled from their base in the southeastern city of Diyarbakir after the air raids on the Free Syrian Army's headquarters in Ras al-Ain.
Shells landed in the Turkish town of Ceylanpinar, which abuts Ras al-Ain, triggering panic, the sources said. It was not immediately clear whether the shells were fired by forces loyal to President Bashar al-Assad or by the rebels.
Turkey, a major backer of Syria's opposition, has asked NATO
for Patriot surface-to-air missiles to be positioned near its 900-km border with Syria as a defensive measure.
Ankara is concerned about its neighbour's chemical weapons, the growing refugee crisis on its border, and what it says is Syrian support for Kurdish militants on its soil.