A suicide attacker has detonated a car bomb near a Syrian security compound in a remote, predominantly Kurdish town, killing at least four people.
Opposition activists said at least eight Syrian intelligence agents were killed and several dozen people wounded in the attack in the north-eastern town of Qamishli, more than 435 miles from the capital Damascus.
Syria's more than two million Kurds have mainly stayed out of the fighting, though some have participated in protests against the regime of President Bashar Assad.
The uprising against Assad that erupted 18 months ago has gradually morphed into a bloody civil war. The conflict has killed more than 30,000 people, activists say, and has devastated entire neighbourhoods in Syria's main cities, including Aleppo, the scene of intense fighting today.
The leaders of Turkey and Egypt, among Assad's main foreign foes, sent stern warnings to the regime and its allies, in speeches to Turkey's ruling party.
Egyptian President Mohammed Morsi said that "we will be on the side of the Syrian people until the bloodshed ends, the cruel regime is gone and Syrian people reach their just rights".
Turkish Prime Minister Recep Tayyip Erdogan urged Syria's allies Russia, China and Iran to end their support for Assad, warning that "history will not forgive those who stand together with cruel regimes".
There was no immediate claim of responsibility for the blast. Syrian state media said the explosion went off in an area housing security officers. It said four people were killed, dozens wounded and nearby buildings damaged.
The Observatory said eight Syrian intelligence agents were killed and at least 40 people wounded in the explosion.
Most Kurds live in the northeast, but Aleppo and Damascus also have Kurdish-dominated neighbourhoods.