EL PASO, Texas -

Human smuggling has started to comprise a larger share of the cash fueling Mexico's warring cartels, according to U.S. agents familiar with the anti-smuggling Operation Coyote.

The cartels generated about $50 million from smuggling in the last six months as the illicit business grows with the surge of Central American migrants seeking to cross into the United States, the Dallas Morning News reported.

That money has helped sustain the Gulf cartel during a violent internal split, officials said. Some factions of the Gulf cartel are now working with the Sinoloa cartel, while another faction has joined the Zetas, increasing bloodshed at the border.

"I'm not suggesting that the cartels have abandoned their drug-smuggling activities," says Oscar Hagelsieb, the assistant special agent-in-charge of Homeland Security Investigations in El Paso. "But with all the money to be made in human smuggling, they clamped their claws into it as well. Big time."

Leaders of other cartels in the region are also heavily involved in smuggling alien migrants, Hagelsieb said.

Some 63,000 undocumented child migrants have been detained at the border since October.

Smugglers have raised their fees from an average $6,000 to more than $8,000, according to a U.S. agent speaking on the condition of anonymity.

Demand for assistance in making the journey through Mexico and over the border could rise further if Mexico implements a plan to speed up freight trains and monitor them with satellite cameras in order to discourage migrants from hitching a ride.

Authorities have watched Mexican cartels diversify since the mid-2000s from mostly drug smuggling to other illicit businesses, including counterfeiting goods, kidnapping, extortion and human smuggling.

Guadalupe Correa-Cabrera, chairwoman of the government department at the University of Texas at Brownsville, foresees new groups getting involved in human smuggling as the business has "become much more profitable."