Thousands of protesters have gathered outside Kuwait's parliament to denounce voting law changes and to rally around calls to boycott next month's parliamentary election.

Rights groups estimate 18,000 people joined the peaceful demonstration Sunday, the latest sign of the Gulf nation's deepening political crisis.

Opposition groups led by Islamists say they will stay away from the polls Dec. 1 to protest a decree by Kuwait's ruler that ended a complex election system in favor of a one-person-one-vote method.

They claim the emir overstepped his authority by making the changes.

Such a move could further deepen Kuwait's political clashes between the Islamist-led opposition and the Western-backed rulers.