Beirut (AFP) - Empowered by an effective fighting force on the ground, a newly-formed Kurdish-Arab alliance in Syria is working to position itself as a player in any future peace negotiations with Damascus.

Top international envoys gathered in New York on Friday to push towards a resolution to Syria's nearly five-year war and discuss the formation of an opposition delegation for talks with the regime.

Although less than three weeks old, the Syrian Democratic Council (SDC) is keen to secure a role in that delegation.

The SDC's speedy rise to prominence comes from its links to the Syrian Democratic Forces, a coalition of Kurdish and Arab fighters battling jihadists in northeast Syria.

The SDF is dominated by the powerful Kurdish People's Protection Units (YPG), the armed wing of the Democratic Union Party (PYD).

Since October, the SDF has pushed back Islamic State group fighters from swathes of land in Hasakeh province -- with the help of air strikes from the US-led coalition.

And in early December, Kurdish, Arab and other political figures gathered at a two-day conference inside Syria to create the SDC as the political branch of the SDF.

It is the SDF's "military weight," Syria analyst Thomas Pierret told AFP, that has made the SDC a force that cannot be ignored in peace talks.

- SDC 'cannot be overlooked' -

The SDC's formation coincided with a landmark meeting of representatives from Syria's armed and political opposition in Saudi Arabia.

The Riyadh conference saw anti-regime factions agree to negotiate with Syrian President Bashar al-Assad while insisting he must step down at the start of a transition period.

They created a 33-member "supreme committee" to select members of a future negotiating team.

But the meeting in Riyadh excluded both the PYD and the YPG, whose relations with most Arab rebel groups have been tense.

Activists and opposition factions accuse the YPG of cooperating with government troops and of ethnic cleansing of Arabs in areas under Kurdish control.

But according to a political figure close to the talks in New York, Russia and the United States are considering the SDC's inclusion in an opposition team.

"The Americans found in the Riyadh conference a step forward, but it wasn't enough," the source said.

Moscow and Washington will discuss "a united delegation with members of the Riyadh conference and the SDC" in New York, he added.

Samir Nashar, a member of the opposition National Coalition, told AFP of "unconfirmed pieces of information" that a Russian-American agreement would see PYD head Saleh Muslim and SDC co-chair Haytham Manna join the opposition team.

- Syria Kurds dominate council -

"The SDC is a new voice that cannot be overlooked," Manna told AFP by telephone from France.

"We are ready to discuss with the Riyadh body, as a part of the opposition, either to create a joint delegation or to find a path forward," he said.

"The SDC is not an alternative for any of these, but is the nucleus of a democratic, secular front that aspires for a state of law."

Manna himself pulled out of the Riyadh talks in protest at the participation of Islamist groups.

The veteran dissident said the SDC sought a Syria "that has separation of powers, sets limits for the relationship between religion and state, and sees all men and women as equal citizens".

But the SDC's real power, according to analysts, stems from its military branch -- in particular, the seasoned fighters of the YPG.

Manna's participation in the council serves "to provide it with Arab and moderate opposition credentials", analyst Thomas Pierret told AFP.

Despite his experience, Manna's "political weight is insignificant compared to the PYD's proto-state", he said.

Syria expert Fabrice Balanche said: "For the Kurds, who are the essential component of the SDC, the council is a way to have a relationship with the West."