Malaysian authorities are warning of possible violence during what are expected to be large rival political demonstrations early next month.

A loose alliance of lawyers and interest groups known as “Bersih,” or “Clean,” says it will bring tens of thousands of people to the capital on July 9 to demonstrate in favor of electoral reforms ahead of balloting expected within the next year.

A Malay nationalist group known as Perkasa says it will organize its own counter-rally in support of the ruling party. Police have warned that both rallies are illegal, but organizers say they will go ahead anyway.

Bersih last organized a mass rally in 2007, attracting an estimated 30,000 people before police broke up the protest with tear gas and water cannons. The opposition coalition led by Anwar Ibrahim made major gains in elections the next year, ending the ruling party's two-thirds majority in parliament.