Ana Maria, from El Salvador, carries her one-year-old son Mateo as they walk through a field with other asylum-seeking migrants from Central America after they illegally crossed the Rio Grande river into the U.S. from Mexico, in Penitas, Texas, March 31, 2019.

Human smuggling from Central American countries to the U.S. reaped revenue of between $200 million and $2.3 billion for smugglers in 2017, but transnational criminal organizations may not be the primary culprits, according to a Rand Corp. report released Monday.

President Donald Trump recently moved to cut foreign aid to the Northern Triangle countries of Central America — Guatemala, Honduras and El Salvador — and in January claimed "ruthless coyotes and vicious cartels" are taking advantage of thousands of children who make the journey up to the U.S. border. Trump also cited human trafficking in February when he declared a national emergency at the U.S.-Mexico border, freeing up billions of dollars for his border wall.

"We learned that human smuggling involves many different types of actors and that we could not credibly distinguish most criminal organizations' activities and revenues from those of other actors, including ad hoc groups and independent operators, that engage in human smuggling," said Victoria Greenfield, lead author on the report and a senior economist at the nonprofit think tank. "At best, we could provide a broad range for the revenues to all types of human smugglers."

"Although our findings are subject to a high degree of uncertainty, they represent a contribution to the evidence base informing ongoing U.S. government efforts to address threats to homeland security posed by TCOs and other actors that participate in human smuggling," Rand said.

Also, Rand said because human smuggling operations are often independent and without "formality and strict hierarchical structures," it might be difficult for the U.S. government to target them with sanctions or other measures effectively.

"Loose networks are difficult to disrupt, ad hoc groups are even less susceptible, and independent operators are easily replaceable," the report concluded. It added that even if the U.S. government "can apply sanctions to some individuals in a given network or group or to individuals who operate independently, its ability to disrupt their organizations or affect the market may be limited."

Rand's 78-page report follows a study it conducted that was sponsored by the Department of Homeland Security. The study looked at revenues earned by human smugglers, as well as taxes levied on migrants by drug-trafficking organizations on routes they control.

"DHS has long warned of the dangers of trafficking and its horrendous impacts on the victims," DHS press secretary Tyler Houlton said in an emailed statement. "Transnational criminal organizations and other human smugglers are driven solely by illicit profit and do not care about human life."

According to Rand, the smuggling of unlawful migrants from the Northern Triangle region to the U.S. generated between $200 million and $2.3 billion for smugglers in 2017. It said the wide range reflects uncertainty about the number of migrants that journey northward, their use of smugglers and the fees they ultimately pay.

Rand estimated that migrants or their handlers paid drug-trafficking organizations taxes, or pisos, of $30 million to $180 million for crossing through their territories in 2017.

The report said cartels or TCOs sometimes "coordinate migrants' border crossings to divert attention from other illicit activities, and they recruit or coerce some migrants to carry drugs."

Rand estimated that the human smugglers charge migrants between $6,000 and $10,000 for their services. It said fees vary greatly and depend on whether migrants want to be smuggled into the interior of the U.S. or turn themselves in to border officials and seek asylum.

The study also estimated the flow of unlawful migrants from the Northern Triangle countries to the U.S., relying in part on government data. It estimated the unlawful migration from Guatemala, Honduras and El Salvador was at least 218,000 in 2017 but could have been as high as about 345,000 between ports of entry.

A caravan of Central American migrants became an issue in last year's midterm elections after Trump deployed more than 5,000 troops to the U.S.-Mexico border. Reports have suggested the migrants are fleeing violence and, in some cases, economic hardship in their home countries.

Last month, the U.S. signed a "regional compact" with the three Northern Triangle countries aimed at addressing what the agency called "the migration crisis." It said the agreement included collaboration to combat human trafficking and migrant smuggling, as well as countering gangs and organized crime activities.

About one-quarter to two-thirds of unlawful migrants from the Northern Triangle region might have hired smugglers in recent years, according to Rand.

The Rand study found that human smuggling can involve taxis, charter buses and tractor-trailers that ferry migrants from the Northern Triangle to locations further north on the journey to the U.S.-Mexico border.

The report also said human smugglers "rely on corruption to protect their activities in the form of bribes to officials." Also, it said "more organized [smuggler] networks can feature transnational organizational structures, but relatively few appear to meet the bar of being 'self-perpetuating associations.'"