The leader of a Haitian gang that kidnapped a group of North Americans over the weekend has threatened to execute them in a video posted to social media on Thursday.

"I swear by thunder that if I don't get what I'm asking for, I will put a bullet in the heads of these Americans," Wilson Joseph, leader of the 400 Mawozo gang said in the video, speaking in front of coffins purported to be those of fellow gang members killed by police.

The kidnappers have demanded $1 million per person for their release.

The group of 17 U.S. and Canadian missionaries and their children was kidnapped in broad daylight on Saturday while on a visit to an orphanage in an area of Port-au-Prince that is reportedly under the gang's control.

(With input from Reuters and AFP)