The announcement is likely to anger neighbouring Turkey and has complicated peace talks in Geneva aimed at ending the five-year civil war.

The United States, a key backer of Kurdish fighters in the battle against the Islamic State jihadist group, has also warned it would not recognise any self-ruled Kurdish region within Syria.

More than 150 delegates from Kurdish, Arab, Assyrian and other parties meeting in Syria agreed to create a "federal system" unifying territory run by Kurds across several Syrian provinces.

"We have given our blessing for the establishment of a federal system in Rojava (three Kurdish cantons) and northern Syria," said Aldar Khalil, a member of the conference's preparatory committee.

Sihanuk Dibo from Syria's leading Kurdish faction, the Democratic Union Party (PYD), said delegates to the conference "approved" the plan.

The announcement came on the second day of the meeting in Rmeilan, a border town in Syria's northeast Hasakeh province.

Kurdish parties already operate a system of three "autonomous administrations" in Syria's north, with independent police forces and schools.

The three cantons stretch along Syria's northern border with Turkey and are known as Afrin and Kobane, both in Aleppo province, and Jazire in Hasakeh province.

The Kurdish People's Protection Units (YPG) is considered one of the most effective forces fighting IS and has cleared the jihadists from swathes of territory in those areas.

Turkey considers the YPG to be the Syrian affiliate of the Kurdistan Workers' Party (PKK), an outlawed group that has waged a decades-long insurgency against Ankara.

- Regime, opposition object -

The new "federal system" is expected to centralise governance in the three cantons under councils elected by the people.

A copy of the conference proposal obtained by AFP said Kurds had "accumulated administrative, social, and institutional experience" by running the cantons.

"For this reason, the establishment of a democratic federation in Rojava - Northern Syria is necessary to coordinate among the autonomous administrations."

Borders and other administrative details concerning the region would also be discussed on Thursday, officials said.

They stressed the federal region would be based on "territorial" lines, not ethnicity, and was not intended as a step towards full independence.

The Kurds, who represent about 15 percent of the Syrian population, have tried to avoid confrontation with the regime or non-jihadist rebels since the war broke out in 2011.

Even so, their declaration of a federal region has angered Syria's government and opposition.

Citing a foreign ministry official, Syria's state news agency SANA said the Kurdish announcement "has no legal basis" and would "encroach on Syria's territorial unity".

The High Negotiations Committee, the main opposition grouping involved in peace talks in Geneva, also rejected the proposal as a "misadventure".

The PYD has not received an invitation to negotiations taking place in Switzerland, to its dismay.

"The Geneva talks will not succeed without us. We are on the ground, fighting Daesh (IS), protecting our region, and running its affairs," Kurdish delegate Aldar Khalil told AFP.

"All these factors make it difficult for us to fit into the Syrian equation. We are committed to a federal system," Khalil said.

In northeastern Syria, Kurds said the move was a natural step.

"The whole region is heading towards federalism. Syria can never go back to the way it was before," said Jawan Bakhtiyar, 31.

Zana Ibrahim, 38, said the announcement would not change much for him since he already lives under the autonomous Kurdish administration.

"But externally, it will be valuable through the formal recognition that this federation will get," he said.

US State Department spokesman Mark Toner said Wednesday that Washington "won't recognise any self-rule autonomous zones within Syria".

Washington-based analyst Mutlu Civiroglu said the Kurdish announcement was a political message "to the United Nations, the US, Russia, and especially to Geneva, that if you ignore us, we are going to determine our future by ourselves."