A battalion of military police escorted sanitation workers in Rio de Janeiro after the city's biggest yearly event was marred by stinking rubbish.
Mayor Eduardo Paes announced the protection after refuse collectors received threats from co-workers who have been striking over pay since last Saturday, the first day of the Rio Carnival.
Revellers navigated through piles of rubbish reeking of urine while dancing samba at street parties known as blocos. The carnival ended on Wednesday.
Paes added that some buses carrying cleaners to the city's famed Sambodrome had been intercepted by men wielding pistols. Streets around the venue have been awash with rubbish.
The conflict highlights Rio's vulnerability to public service disruptions as it prepares to host the final of soccer's World Cup in July and the Summer Olympic Games in 2016.
A wave of protests and vandalism sparked by bus fare increases shut parts of Rio and other Brazilian cities on and off for weeks last year.
Teachers and bank workers have also gone on strike.