Bolivia's pro-government supporters and security forces confronted protesters loyal to former president Evo Morales in a street melee Sunday, the second such violent escalation this week as fears grew of further unrest in the Andean nation.

Bolivia’s socialist President Luis Arce defied an ultimatum from his bitter rival as their supporters attacked each other with stones and fireworks, bringing turmoil to the streets of La Paz on Monday.

Thousands of anti-government demonstrators marching in support of Bolivia’s former socialist President Evo Morales were clashing with counterprotesters blocking their way, a stark sign of an escalating power struggle in the volatile Andean nation.