Five employees of UNICEF, the United Nation’s children’s organization, were released Monday night after being held by a gang for three weeks in Haiti, where criminal groups are turning to kidnappings to finance their criminal enterprises.

Six people were kidnapped on July 7 during an authorized UNICEF mission in an area controlled by armed groups in Port-au-Prince, the capital, and one was released the following day, UNICEF said in a statement.

The agency did not say whether any ransom was paid.

Haitian gangs are abducting people for ransom to buy weapons and ammunition as they tighten their violent grip on the capital and surrounding areas. Experts say that gangs are leaning more heavily on their own revenue sources, like extortion, imposing road tolls and kidnappings, allowing them to rely less on elite business leaders, who have traditionally supported them.

Nearly 350 people were kidnapped in the first six months of this year, according to U.N. figures. The U.N. said 1,494 people were kidnapped in 2024, a year that saw a major surge in gang violence.

While there may have been more kidnappings last year, the trend has been on an upward climb over the past few years.

Nearly 300 kidnappings were reported in the first six months of 2023, a figure that matched the total number of documented cases the previous year and was nearly three times the number reported in 2021, according to UNICEF.

Many of the kidnapping victims were women and children, the U.N. said.

Even those numbers may be an undercount. Many kidnappings go unreported, because of fear, a lack of trust in the authorities and systemic corruption, said Austin Holmes, a Haiti-based humanitarian and security expert who has helped negotiate the release of hostages in Haiti.

“Fewer than 10 percent of kidnappings are ever officially recorded,” Mr. Holmes said. “The true scale is staggering — likely ten times higher than what’s reported and documented.”

The number of kidnappings has risen steadily since 2018, particularly as gangs increased their control over the Haitian capital and surrounding region, he said.

“We expect kidnapping to remain prolific while gangs control the country, and operate with impunity,” he said. “It’s one of their three primary means of revenue to sustain their power and control.”

Ransoms vary wildly and are typically much higher for foreigners, experts said.

Jeff Frazier, an American who runs a nonprofit organization in Haiti and was kidnapped in 2023, said kidnapping is becoming more common among gangs that do not have other steady streams of revenue, such as tolls or drug trafficking.

“If you don’t control a road, then you don’t have income, and so you have got to come up with money some other way,” Mr. Frazier said.

Like the UNICEF employees, Mr. Frazier was held by Renel Destina, known as “Ti Lapli,” a gang leader who controls the Grande Ravine area of Port-au-Prince, the police said. He was held with about a dozen others for 43 days.

Most victims must pay ransom multiple times until they have convinced their captors that no more money is available, Mr. Frazier said. The hostages’ families are often sent photographs, audio or video of hostages being tortured as a means of drumming up more, he said.

“Some people pay three, four ransoms,” Mr. Frazier said.

The gangs generally do not kill their captives, because then they would not get paid for them.

Mr. Frazier said he was surprised that the UNICEF employees were released after just three weeks and wondered whether a threat of retaliation from American private military contractors, who are increasingly operating in Haiti, was used as a pressure tactic in negotiations.

In March, U.S. federal prosecutors in Washington charged Johnson Andre, known as “Izo,” the leader of the 5 Segond gang, in the March 2023 armed hostage taking of a U.S. citizen who was held for ransom.

He has not been apprehended.

In May, Germine Joly, who the F.B.I. said led the 400 Mawozo gang in Haiti, was convicted in Miami of organizing the kidnapping of 16 U.S. citizens in 2021 and holding them hostage for more than two months.

He is serving a 35-year sentence for a different U.S. federal gun trafficking case but has not yet been sentenced for the kidnapping.

The UNICEF employees are receiving medical attention and psychological support and have been reunited with their families, UNICEF said.

“Humanitarian workers are not and should not be a target,” UNICEF said. “They provide lifesaving support to the most vulnerable, including children and families caught in crises. We call on all actors to respect and protect humanitarian personnel, in line with international humanitarian law.”

André Paultre contributed reporting from Port-au-Prince.