Eleven civilians, including eight children, were killed on Saturday in Haiti’s capital when drones aimed at a gang leader struck a birthday party where community members had gathered, a human rights group said.

In March, the authorities in Haiti hired foreign military contractors to operate armed drones to target gangs that terrorize the capital, Port-au-Prince. The contractors work for a company owned by Erik Prince, a prominent supporter of President Trump.

Experts have warned that the strikes were not only a violation of international law, because there is no officially declared armed conflict in the country, but also bound to inflict collateral damage in densely populated urban areas where gang members operate.

While two police officers were accidentally killed by a drone last month and two civilian adults died in drone strikes in June, Saturday’s episode was believed to be the first time children were among the victims.

Two “kamikaze” drones were deployed Saturday evening in Simon Pelé, a gang-controlled area in Cité Soleil, a large, impoverished neighborhood near Port-au-Prince’s airport, according to the National Human Rights Defense Network.

The target was Albert Steevenson, a gang leader also known as Djouma, who was celebrating his birthday and distributing gifts to children, the human rights group said. Mr. Steevenson escaped unscathed.