Dozens of Syrian opposition factions on Friday condemned a PYD/YPG declaration of a federal region in the war-ravaged country's north as a step towards partition.

"We categorically reject the declaration... regarding an autonomously-run or federal region in northern Syria and we consider it to be a dangerous step aimed at partitioning Syria," some 70 opposition factions said in a statement posted online.

"The unity of Syria's people and land, and our rejection of any plans for partition or any other design that could lead to partition... constitute a red line," they said.

PYD/YPG groups on Thursday announced a "federal system" to unite areas under their control across several provinces in the country's north.

The declaration was swiftly shot down by the High Negotiations Committee, the main opposition grouping, and by the regime, both in Geneva for peace talks to try to end Syria's five-year war.

And opposition groups on Friday threatened to use "all the political and military force" at their disposal to counter the announcement.

They likened the PYD/YPG declaration to the Daesh terrorist group's bid to carve out a self-styled "caliphate" from swathes of territory under its control in Syria and Iraq.

"Several groups have taken advantage of the Syrian people's revolution and their sacrifices and taken control of parts of Syrian territory to set up ethnic, nationalist and sectarian entities," their statement read.

"The first of these plans was the one executed by Daesh," it added.

Signatories to the statement included the powerful Jaish al-Islam (Army of Islam) and the Jabha Shamiya (Levant Front).

The PYD/YPG control over 10 percent of Syria's territory and three-quarters of its border with Turkey.

The PYD/YPG have however been excluded from the U.N.-mediated Geneva process that has brought regime and opposition representatives together for indirect negotiations.

On Friday, hundreds of demonstrators took to the streets across opposition strongholds in Syria to mark the fifth anniversary of the outbreak of the revolt against Bashar Assad's regime.

Along with the three-starred, tricolour flag used by the opposition, activists in the war-ravaged city of Aleppo held up a banner that read: "Down with federalism."