The latest incidents bring the death toll in the ethnic violence, which erupted at a football match on Friday, to at least 25. Hundreds more are reported injured.

The tension in the area, a wedge of land bordering Turkey and Iraq, has been heightened by Iraq's interim constitution, which guarantees Kurdish rights.

"Many of the Kurdish people in Syria do not enjoy civil rights and are stateless - they are looking for similar rights to the Kurds in Iraq," Ibrahim Alcholbec of the Kurdish Syrian Human Rights Project in Yorkshire said.

Syria fears that Iraq's newly empowered Kurds will encourage and even materially support their brethren.

The scale and duration of the violence is the most serious in Syria for many years.

"It's relatively significant," said Sarah Meyers, an analyst at the security consultancy Control Risks. "Any demonstration or riot in Syria is usually put down very quickly but this has carried on for several days."

Damascus faces other pressures: Washington is preparing to impose sanctions and Syrian frustration at Bashar al-Assad's inability to reform the old guard since he inherited the presidency four years ago is increasing.

The unrest began in the mainly Kurdish town of Qamishli where fans of an Arab team taunted fans of a largely Kurdish team by waving pictures of Saddam Hussein.

As the fighting spread to several towns nearby officials accused Kurdish leaders for turning a soccer riot into a political issue.

Yesterday Mr Alcholbec accused Syrian intelligence and the Ba'ath party of instigating the violence. About 100 Kurdish shops, as well as many cars, were set on fire in the city of Hasakah, he said.