* Anti-Assad groups in truce after fighting near Turk border
* Kurds await release of kinfolk by anti-Assad Islamists
* Assad forces, rebels in unusual battle along Syrian coast
Syrian Kurdish forces freed a local leader linked to al Qaeda as part of an agreed ceasefire to end fierce fighting with Islamist rebels in the northern Syrian town of Tel Abyad on Sunday, activists said.
In return, Islamist rebels have promised to release hundreds of Kurds taken hostage as collateral from the leader of the Islamic State of Iraq and Sham (ISIS), known as Abu Musaab.
The sporadic fighting in the northern Syrian border region over the past five days has signalled a growing power struggle as Islamists work to cement control of rebel zones while Kurds assert their autonomy in mostly Kurdish parts of the region.
The tensions highlight how the two-year insurgency against 43 years of Assad family rule is spinning off into strife within his opponents' ranks, running the risk of creating regionalised conflicts that could destabilise neighbouring countries.
Pro-opposition activists said that Turkish military forces had been reinforced on Turkey's side of the frontier near Tel Abyad on Sunday, but the Turkish army could not be reached for comment. Turkish forces exchanged fire with Syrian Kurdish fighters in another border region earlier this week.
The Syrian Observatory for Human Rights said the fighting in Tel Abyad started when the local brigade of the Qaeda-linked ISIS asked Kurdish Front forces, who have fought with the rebels against Assad, to pledge their allegiance to the ISIS leader there, which they refused.
Other activists said the clashes were an outgrowth of fighting that broke out last week in other parts of the northern border zone, spreading conflict to Tel Abyad.
The Observatory said Kurdish forces were still awaiting the awaiting the release of hundreds of Kurdish residents kidnapped by Islamist fighters. Many of the hostages were relatives of Kurdish fighters in the area, it said.
The clashes in Tel Abyad came to head early on Sunday when Kurdish fighters surrounded a building housing Abu Musaab, who threatened to blow himself up if the militants tried to enter.
FIGHTING IN ASSAD'S COASTAL STRONGHOLD
Opposition activists also reported a rare eruption of fighting between Assad's forces and rebels in the Mediterranean coastal province of Tartous, an enclave of Assad's Alawite minority sect that has remained largely unscathed by the war.
The fighting broke out on Saturday evening near the Sunni town of Banias, the site of a massacre of dozens of people only a few months earlier by Alawite militias loyal to Assad.
The anti-Assad revolt has evolved from its origins as a peaceful protest movement in March 2011 into a civil war that has killed over 100,000 people and turned markedly sectarian.
Syria's marginalised Sunni Muslim majority has largely backed the insurrection in the major Arab state while minorities such as the Alawite sect, an offshoot of Shi'ite Islam, have largely supported the president.
The ethnic Kurdish minority, meanwhile, has been alternately battling both Assad's forces and the Islamist-dominated rebels. Kurds argue they support the revolt but rebels accuse them of making deals with the government in order to ensure their security and autonomy during the conflict.
Scattered over the territories of Iran, Turkey, Iraq and Syria, the Kurdish people are often described as the world's largest ethnic community without a state of their own.
Before the Tel Abyad truce was mediated by other rebel units, hundreds of residents fled the town. The opposition group Hassaka 24 posted on its website that the Nusra Front, another Islamist militant faction with ties to al Qaeda, had been firing anti-aircraft rockets at Kurdish positions in the area.
Residents on Turkey's side of the border said many injured people were being brought over from Tel Abyad for medical care.