The United Nations peacekeeping mission in Haiti is investigating reports that dozens of prisoners were shot during a jail riot soon after the 19 January earthquake.
A New York Times investigation alleges at least 12 unarmed prisoners were killed by Haitian police in the city of Les Cayes after they had surrendered.
Haitian police have blamed fighting among inmates for the deaths. Thousands of prisoners escaped from jails in Haiti in the chaos after the quake that killed more than 230,000 people.
'Strewn with bodies'
The newspaper said the riot started when some of the 467 inmates tried to escape from the overcrowded jail in Les Cayes, Haiti's third biggest city.
However their way out was barred when Haitian police and UN peacekeepers surrounded the jail.
After inmates rampaged for hours police went in, throwing tear gas grenades.
The New York Times says that after the compound was stormed, "dozens of inmates lay dead and wounded, their bodies strewn through the courtyard and crumpled inside cells."
It alleges that Haitian forces shot unarmed inmates and then tried to cover it up.
However local officials in Les Cayes said lethal force had not been used when the police went in. They blamed the deaths on a ringleader in the jail.
The New York Times said it appeared 12 to 19 prisoners had been killed and up to 40 wounded by gunshots.
A UN spokesman, David Wimhurst, told AP news agency that the UN had opened an internal inquiry and that a more extensive formal inquiry was possible.
"As far as we're concerned there was a major human rights violation in that prison", he said.