Drug gangs and their hitmen -- groups such as the Aztecas and the Mexicles -- often continue their battles behind bars in the city, located across the border from El Paso, Texas and right at the heart of Mexico's raging drug war.

Where tensions run high, walls have climbed higher to try to stop rival Mexican gangs from taking the blood-stained chaos from the streets of Ciudad Juarez with them into prison.
Drug gangs and their hitmen -- groups such as the Aztecas and the Mexicles -- often continue their battles behind bars in the city, located across the border from El Paso, Texas and right at the heart of Mexico's raging drug war.
"The (six-meter, 20-foot) walls went up in late 2009," prison spokesman Hector Conde told AFP.
"Before, there were only chain-link fences that inmates would jump over pretty easily. There were riots all the time," often leaving dozens dead and requiring helicopter-backed security operations to break them up, he said.
Conde declined to enter the block housing members of the Aztecas, a notorious gang of hitmen for the Juarez cartel.
"Some of the Aztecas were just moved to another facility recently, so these guys are really aggravated. They could carry out reprisals if you go in there," he warned.
Across the way, out of sight, were members of the Mexicles gang. They work for the Sinaloa cartel led by Mexico's most famous fugitive, Joaquin "El Chapo" (Shorty) Guzman.
Officials blame the Juarez and Sinaloa cartels for most of the violence in Juarez as they fight for control of the lucrative drug trafficking routes into the United States.
Last year, 3,100 people died in violent attacks in this northern city of some 1.2 million -- roughly 60 each week on average.
A surge of drug-related violence has left almost 35,000 people dead in Mexico since the government of President Felipe Calderon launched a military crackdown on the cartels in 2006, according to official figures.
The murder rate climbed to more than 10 a day in Juarez in February 2009, prompting Calderon to deploy more than 5,000 troops to the city. Things were calmer for a few months but the killings soon picked up again.
Some of the murders are particularly gruesome, decapitated bodies, corpses hung from bridges. Children, even pregnant women, have been among the dead but most are young gang members.
With factory salaries starting at less than $50 a week, the financial lure of the drug gangs is huge in Juarez -- one of the main thoroughfares for the cocaine that feeds the ever-strong US market.
Physical separation may help prevent jailed gang members from starting riots, but critics warn against maintaining gang labels behind bars.
"That gives them territory inside the prison and makes it an extension of what is happening outside on Ciudad Juarez streets," Gustavo de la Rosa, from the Chihuahua state human rights commission, told AFP.
The gangs work with military-style organization and often control the jails imprisoning them, he said.
After checking no one was listening, a guard told AFP there were around 2,400 inmates at the prison, 700 of them Aztecas housed in one block.
The prisoners were separated based on tattoos linking them to their gangs: the Aztecas with pyramids and Aztec symbols and the Mexicles sporting skulls and their gang name, said prison pastor Victor Martinez.
Tensions were lower in his section of the jail, which the prison authorities had decided was the best place to house convicted evangelical Christians.
"I feel safer here than on the streets or other parts of the prison," said Otoniel Lucero Pena, a 46-year-old in for trafficking marijuana. He said he had never belonged to a gang.
Prisoners such as Pena gained most from the wall, Martinez said.
Five years ago, the Aztecas tried to make some of the evangelical prisoners work for them. When they refused, they attacked them, Martinez said.
"They started to beat drums to signal the start of a riot or clash. Then they jumped over the metal fence of the Christians' sector, where there were 140 prisoners at the time. They killed three of them but the others managed to escape to the women's area."