At least 24 public buses have been burned in less than 24 hours in the southeastern Brazilian state of Minas Gerais.

Authorities said Monday that the attacks began Sunday afternoon and continued through the night in the state capital of Belo Horizonte and more than a dozen other cities. The motive for the attacks so far is unclear.

Military police in Minas Gerais say it's also unclear if the attacks were coordinated by criminal groups, or if solo actors were committing copycat crimes. Drug gangs sometimes burn buses in retribution for police operations against them.

Brazil frequently struggles to curb bursts of violence. Earlier this year, a wave of violence prompted the military to take over security in Rio de Janeiro, which borders Minas Gerais.