A number of fierce battles between jihadists and armed Kurdish groups in Syria have added another layer to what is increasingly being described as a civil war within a civil war.
The Kurds became the first anti-government group to have actively taken on the jihadists, inflicting high casualties on fighters of two al-Qaeda affiliated groups, the al-Nusra Front and the Islamic State of Iraq and the Levant.
Friction with the jihadists worsened as the militants, who had led a violent campaign to set up Islamic mini-states in northern Syria, tried to extend their power from Raqqah province to oil-rich territories held by secular Kurdish groups.
Rami Abdul Rahman, of the Syrian Observatory for Human Rights, the UK-based pro-opposition group, told the BBC the latest fighting was sparked by an attack on a group of Kurdish women fighters in July by the al-Nusra Front in northern Hassakeh province.
Militants from the country's most powerful Kurdish party, the Democratic Union Party (known by its Kurdish acronym PYD), responded to the attacks by driving out al-Qaeda-affiliated and Salafist groups from the north-eastern town of Ras al-Ain, taking control of a border post with Turkey.
As the fighting escalated at the end of July, jihadists also reportedly killed hundreds of Kurdish civilians.
The US joined Russia in condemning the attacks on the civilians in the towns of Tal Aran and Tal Hasel, south-east of the city of Aleppo.
Prominent Kurdish politician Isa Huso was also killed by the militants.
Since the uprising against President Bashar al-Assad began in Syria in March 2011, the Kurds have largely sought to keep the fighting out of the areas under their control, by avoiding conflict both with the regime and the opposition.
The recent fighting with the jihadists in effect ends this tactic, which had allowed Kurds to consolidate their power in several cities across northern Syria.
Salih Muslim, head of the PYD, has reassured the Syrian opposition as well as Turkey that the de-facto autonomy of the areas under its control is temporary, lasting only until the rebellion reaches its goals, and that it is not seeking to set up an independent Kurdistan in Syria.
The hostility against the Kurds within the armed uprising in Syria is not limited to jihadists.
Col Abdel Jabbar al-Oqaidi, head of the military council of the Free Syrian Army (FSA) in Aleppo, recently accused the PYD of siding with the government and vowed in a video statement to destroy it.
Mr Muslim insists the PYD is part of the revolution and points to the comrades who have lost their lives fighting alongside the FSA against Syrian troops in Aleppo and other towns.
The Kurds are Syria's largest ethnic minority, making up more than 10% of the population at between two and three million people, concentrated largely in the north of the country.
Deprived of most of their civil rights under Baathist rule in Syria, the Kurds were rebelling long before the latest uprising.
In 2004, dozens of Kurdish activists were killed during a riot in the north-eastern city of Qamishli.
"The Qamishli massacre didn't spark solidarity among the Arab population at that time," says Mr Muslim. "The Syrian people shouldn't forget that Kurds started their uprising against the regime long before the Arabs."
It is not just the Kurds that jihadists have clashed with.
There has been sporadic fighting between them and other rebel groups in Syria.
Al-Qaeda linked groups have killed several commanders of the Free Syrian Army, most notably Kamal Hamami, a member of the Supreme Military Council, who died in early July.
Despite the killings and talk of vengeance, the FSA has yet to declare a war on jihadist groups.
But compared to the loosely-organised battalions of the FSA, the jihadists would find fighting the 10,000-strong Kurdish militias long term much more difficult.
Added to the mix is Iraqi Kurdistan. The president of the autonomous Kurdish Regional Government, Massoud Barzani, has warned jihadists he could intervene directly to protect Syrian Kurds.
Turkish officials are also deeply uncomfortable with the gains of the PYD, which has close ties with the Kurdistan Workers Party (PKK) which fought decades of war against Turkey.
Syria's Kurds, for their part, accuse Turkey of assisting jihadist groups, which have a strong presence in areas closer to the Turkish border.
The Turkish government is currently in peace talks with the PKK but it still wants to prevent Kurds from strengthening their hand at the negotiating table by achieving de-facto autonomy in Syria.
Nevertheless, the official invitation to Mr Muslim to visit Turkey may suggest a positive shift in Turkish policy towards Syria's Kurds.
When President Assad pulled his forces out of Kurdish areas last year it was principally to concentrate on fighting elsewhere.
But part of the logic was to pit the Kurds against the Turkish government.
With the announcement of Turkey's talks with the PKK, this logic has largely failed.
Nevertheless, the current situation remains to the advantage of the regime, as the infighting between Kurds and rebels in the north will disrupt the fight against Assad forces in the south.