The kingpin demands a total of $17 million in exchange for the hostages, which include 17 US and Canadian missionaries and their children.
The leader of a Haitian gang who kidnapped a group of North Americans over the weekend has threatened to execute them.
In purported footage shot on Wednesday but released on Thursday on social media, a man named Wilson Joseph, wearing a purple suit and surrounded by armed men, stands in front of coffins containing the bodies of five members of his gang.
"Since I'm not getting what I need, I'll kill these Americans," Joseph said, speaking in Haitian Creole.
A senior US official speaking on condition of anonymity said the video appeared to be genuine.
"As far as I know, the video that appeared online today is legitimate," the official told reporters late Thursday.
"It’s not a fake video as far as we can tell right now."
"We are in contact with the Christian Aid Missionaries. We are in contact constantly with Haitian National Police. The FBI is on the ground in Haiti and in contact with all the parties involved," the official added.
The kidnappers are demanding $17 million ransom for the hostages' freedom, said security sources.
How did the kidnapping happen?
On Saturday the group of 17 US and Canadian missionaries and their children were kidnapped in broad daylight while on a visit to an orphanage in the heart of an area in eastern Port-au-Prince, which is under control of the gang.
The Ohio-based Christian Aid Ministries, to which the abducted missionaries belong, said the group included 12 adults aged 18-48, along with five children aged eight months, three, six, 13 and 15.
Since December 2020, Haitian police have sought Joseph for crimes including assassination, kidnapping, vehicle theft and hijacking of cargo trucks.
The United States has advised Americans not to travel to Haiti, in particular, due to kidnappings they say regularly include American citizens.