US officials say there has been a surge of high-powered weapons being smuggled from Florida to Haiti.
The Caribbean country has been rocked by brutal gang warfare in which hundreds of people have been killed in the past six weeks alone.
A US federal agent said that the number of weapons illegally shipped to Haiti had risen to unprecedented levels.
Haitian police have complained about being outgunned and outnumbered in their fights with gang members.
US Special Agent Anthony Salisbury told Miami reporters that “not only have we seen a marked uptick in the number of weapons, but a serious increase in the calibre and type of firearms being illegally trafficked”.
According to Mr Salisbury, there is an alarming trend of high-powered weapons being smuggled from ports in South Florida to the US. “In the wrong hands, these weapons are easily capable of causing mass casualties,” he warned.
In June, the UN Security Council voted to ban the sale of small arms and ammunition to “non-state actors” in Haiti, but the flow of illegal arms seems to have only increased.
On Saturday, customs officials at a port in the Haitian capital seized containers full of ammunition and weapons.
The paperwork for the containers said they were destined for the Episcopal Church of Haiti.
The Episcopal Church has issued a statement saying that it had not been expecting any shipments, but police have since arrested a priest in connection with its investigation.
Haiti is not the first violence-wracked country to complain about the flow of illegal weapons from the US.
Mexico has long demanded that the US do more to combat arms trafficking, pointing out that the vast majority of weapons used in crimes come from the US.
Last year, the Mexican government took the unusual step of suing some of the biggest US gun manufacturers, accusing them of “facilitating the unlawful trafficking of their guns to drug cartels and other criminals in Mexico”.