Fighting between gangs in the Brazilian city of Rio de Janeiro will lead to a "bloodbath" unless the authorities act, Amnesty International has warned.
Rio's slums are wretched, violent places
Turf wars between drug gangs from the city's slums could result in the deaths of many innocent people, the London-based human rights group said.
Hundreds have been forced from their homes since one gang moved into the Vigario Geral area, Amnesty said.
Correspondents say Rio is one of the most violent cities in the world.
Gangs from Vigario Geral and the neighbouring slum of Parada de Lucas have been fighting for 20 years.
On Sunday a group of heavily-armed men from Parada occupied Vigario Geral, expelling dozens of families whom they allege have links with the rival gang, Amnesty said.
"The authorities must restore order to these communities and guarantee the safety of the civilian population," the London-based group said in a press release.
A Rio de Janeiro police spokesman told the Associated Press news agency that many of the evicted residents have returned to their homes.
Ricardo Gouveia said police would keep peace in the area and there was no evidence of casualties in the fighting between drug gangs.
Amnesty disputed the claims.
"Despite their presence in the surrounding area, it appears that the Rio police have not attempted to regain control of either of the favelas (slums) ... despite the clear threats that this situation poses to the civilian population," the group said.
The Vigario Geral slum is the site of a 1993 massacre by police officers, in which 21 people died.