CARACAS, Venezuela — Police used tear gas, plastic bullets and water cannons to scatter hundreds of students protesting against the government Thursday, while President Hugo Chavez's supporters celebrated the 18th anniversary of his failed coup as an army officer.

Caracas Police Chief Carlos Meza said authorities broke up the protest because university students had not been granted permission to march.

He said the denial was aimed at preventing clashes with thousands of "Chavistas" marching across the capital to mark the botched 1992 military rebellion that Chavez led as a lieutenant colonel.

"They don't have permission to march," Meza said.

Student leaders countered that they have the right to stage peaceful protests, and they said authorities loyal to Chavez frequently deny them permission to demonstrate. Before the protest was dispersed, students chanted: "We're students, not coup plotters!"