SAN SALVADOR, El Salvador Every day, as she travels to the food stall she operates, Mirna Isabel Villalta crosses an invisible but dangerous boundary.

Her modest home is in a part of San Salvador controlled by the Mara Salvatrucha, a gang so ruthless and sprawling that the Obama administration has labeled it an international criminal organization. Her food stall is in the city center in an area controlled by Barrio 18, a gang that despises the Mara Salvatrucha.

She knows she's breaking an unspoken rule.

"You can't go from one barrio to the other," Villalta said. But she does. Every day. And she keeps mum to those around her food stall about where she lives.

"They don't know we live in Mara Salvatrucha territory," she said.

El Salvador's capital and indeed nearly the entire country is a checkerboard in which gang territories circumscribe the movement of those in the lower economic rungs of society, and especially young men. When a family lives in an area dominated by one gang, it avoids going to an area controlled by a rival gang.

"The control the gangs hold over their territories has never been so complete. It is without precedent," said Carlos E. Ponce, a criminologist and former adviser to the National Civilian Police.

As the gangs deepen connections with regional organized-crime groups involved in drug, weapons and human trafficking, they present a direct challenge to state control over the tiny Central American nation, Ponce said.

The chaos also provides an incentive for Salvadorans to try to flee north for the safety of the United States. Experts trying to explain the huge increase in children and teens who've arrived in the United States say anecdotal evidence points at least in part to the hold that criminal gangs have in El Salvador, Honduras and Guatemala.

As insecurity extends across El Salvador, gang bosses reach for younger and younger kids to fill their ranks.

"Youngsters don't get in at age 14. They get in at age 10 now," said Luis Romero, the head of a project called Homies Unidos that pulls gang members off the streets to give them skills. "You should see the juvenile jails. They are packed."

In Ilopango, a poor sprawling district southeast of the capital, the local government has set up programs to offer training to young people in driving and speaking English. But district authorities have found they have to duplicate some programs, one for areas controlled by the Mara Salvatrucha and another for Barrio 18 areas.

"We've set up soccer schools in each of their territories," said Rosemberg Hernandez, who's in charge of youth programs in Ilopango. "We do this to avoid problems."

Hernandez said the two gangs had different clothing and hairstyles, even different vocabularies.

"It sounds ridiculous but there are things that Mara Salvatrucha gang members won't say. They never say eight or 18," he said, for fear of referring to the rival gang.

While flight to the United States might be one way people are trying to escape the violence, there's an ironic symmetry: El Salvador's gang problem has its genesis in the United States, from the time of the country's civil war, which also sent tens of thousands of Salvadorans fleeing to the United States.

For young people, that war which wracked El Salvador from 1980 to 1992 and left at least 75,000 civilians dead is ancient history. But by the time peace accords were signed, the gangs were on the rise, formed by gang members who'd been deported from Los Angeles.

"Those kids 18 and 20 years old who joined the gangs have now grown up," said Ilopango Mayor Salvador Ruano. "We've now had at least three generations of gang members."

Salvadoran leaders have tried different tactics to rein in the gangs, beginning with a 2003 program, known as "Strong Hand" and followed by "Super Strong Hand" years later, that swept thousands of gang members into prisons.