The jihadist Islamic State (IS), which has taken over large swathes of war-torn Syria in just a few months, was Thursday engaged in fighting Kurds and members of a Sunni tribe.
The Syrian Observatory for Human Rights said the well-equipped Kurds, who started fighting IS after it emerged in Syria in spring last year, had Wednesday recaptured several hills surrounding the city of Ain al-Arab (Kobane in Kurdish) in the north.
IS has been trying to take Ain al-Arab -- Syria's third Kurdish city -- and incorporate it into the Islamic "caliphate" it proclaimed last month.
The fighting killed 14 members of the Kurdish People's Protection Units (PYG) and 35 IS members. Dozens of other fighters were wounded, the Observatory said.
The fighting comes two weeks after some 800 Kurdish fighters entered Ain al-Arab from neighbouring Turkey to fight IS.
There are some 3.5 million Kurds in Syria, and with the country swamped in a war that broke out three years ago, they are seeking autonomy in areas where they are a majority.
Eastwards, IS pounded regime positions in Hassakeh, as they tried to surround the city of 200,000 Kurds, Arabs, Armenians and other Christians.
- IS fights Sunni tribe -
In the oil-rich eastern province of Deir Ezzor, most of which is under IS control, members of the Shaitat Sunni tribe fought the jihadists, tweeting about an "uprising" against the group.
Fighting erupted after IS detained three members of the tribe, "violating an agreement", it said.
The Observatory said the Shaitat had promised IS it would not oppose it, in exchange for the jihadists not harassing or attacking its members.
The Sunni Shaitat tribe extends across three villages -- Abu Hamam, Kashkiyeh and Ghranij.
On Thursday, a day after fighting erupted, IS members raided the villages, searching houses and kidnapping or "detaining" an unknown number of people, the Observatory said, adding that fighting was raging.
Meanwhile, IS set up new checkpoints in the Deir Ezzor countryside, but gunmen opened fire at one of the posts.
At least five jihadists were killed in the fighting, including a Belgian.
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Syria's war began as a peaceful movement for democratic change, but erupted into conflict after President Bashar al-Assad's regime unleashed a brutal crackdown against dissent.
Months into the fighting, foreign jihadists began entering Syria.
In a statement to the army's magazine on Thursday, Assad characterised the war in his country as a "fight against terrorism," saying he was "more determined than ever to resist the terrorist and colonialist project".
Also on Thursday, the Observatory reported IS had imposed a strict dress code for women in Deir Ezzor, forbidding them showing any part of their bodies.
"Women ... are completely forbidden from showing their eyes," read an IS statement that the Observatory said was distributed in areas under jihadist control in Deir Ezzor province.
Women are forbidden from wearing "open abayas (traditional black gowns) that reveal colourful clothes worn underneath", it said, adding women "must not wear high heels".
It threatened an unspecified punishment for women who violated the dress code, and banned the sale of tobacco products, as well as smoking in public.
- Army shelling kills 17 -
On another front in Syria's complex war, the number of people killed in army shelling on an opposition-held town northeast of Damascus on Wednesday rose to 17, the Observatory said. Among the fatalities were three children.
An AFP photographer in Douma, which has been besieged by the army for more than a year, said shelling had hit several parts of the town, including a busy market area.
"The shelling came suddenly. One minute, children were playing in the market, the next, there were body parts and wounded people everywhere," Abd Doumany said.
The photographer also described graphic scenes at one of the town's ill-equipped field hospitals.
"The wounded were being treated on the floor," he said.
In the northern province of Idlib, jihadists from Al-Qaeda affiliate the Al-Nusra Front took the Sarmada area near the Turkish border after brief clashes with other rebels, the Observatory said.
Following Nusra's capture of the area, government warplanes launched airstrikes on the area, killing at least two people.
Yet another front in Syria's war opened in mid-July between Nusra fighters and various rebel groups, who until then had been allies. Al-Nusra said it intended to establish an "emirate" to rival that set up by IS along the Syrian-Iraq border.