For nearly two decades, Kurds have gathered peacefully in this mountainous corner of northern Iraq to commemorate one of the blackest days in their history. It was here that Saddam Hussein's government launched a poison gas attack that killed more than 5,000 people on March 16, 1988.

So it came as a shock when hundreds of stone-throwing protesters took to the streets here Thursday on the anniversary, beating back government guards to storm and destroy a museum dedicated to the memory of the Halabja attack.

The violence, pitting furious local residents against a much smaller force of armed security men, was the most serious popular challenge to the political parties that have ruled Iraqi Kurdistan for the past 15 years. Occurring on the day the new Iraqi Parliament met for the first time, the episode was a reminder that the issues facing Iraq go well beyond fighting Sunni Arab insurgents and agreeing on cabinet ministers in Baghdad.

Although Kurdistan remains a relative oasis of stability in a country increasingly threatened by sectarian violence, the protests here — which left the renowned Halabja Monument a charred, smoking ruin — starkly illustrated those challenges even in Iraq's most peaceful region.

Many Kurds have grown angry at what they view as the corruption and tyranny of the two dominant political parties here.