(CNN) -- The deportations of thousands of Mexicans who have served time in U.S. jails into Ciudad Juarez, Mexico, are adding a deadly ingredient to an already volatile state of security, Juarez Mayor Jose Reyes Ferriz said.
Juarez Mayor Jose Reyes Ferriz says street level drug dealers are responsible for most recent violence there.
Turf battles between rival drug cartels, and between authorities and cartels, have made Juarez one of the world's most dangerous cities. There were 305 drug-related killings in August, making it the deadliest month yet, according to the mayor's office.
Most of the recent violence has been committed by young street-level drug dealers who work for the Sinaloa or Juarez cartels, Reyes Ferriz said.
Adding deportees from the United States, some with criminal records, worsens the situation, the mayor said.
In the past 45 days, 10 percent of those killed in Juarez had been deported from the United States in the past two years, Reyes Ferriz said.
"We don't have the statistics to know if they were criminals from the United States or not," he told CNN's Rick Sanchez this week. "We know they were deported from the U.S. Most of them come from U.S. jails. They end up in the city of Juarez, and that's a problem generated for us, but also for the United States."
Most deportees are simply Mexicans who crossed the border illegally, but some hardened criminals get involved with the gangs, which have networks in the United States, Reyes Ferriz said.
But according to Immigration and Customs Enforcement, the U.S. agency that oversees deportations, the number of criminal deportees entering Juarez from El Paso, Texas, is not high.
"El Paso had the fewest removals among the other border areas" in fiscal 2008, ICE spokeswoman Leticia Zamarripa said.
About 85,400 "criminal aliens" were deported from the United States to their homelands in 2008, according to ICE.
Of those deported through El Paso, about 6,800 were criminal aliens, Zamarripa said. The term refers to noncitizens who have been convicted of a crime in the United States. Illegal immigrants whose only violation is entering illegally are not classified as criminal aliens, Zamarripa said.
Not all were Mexican, so not all left the United States by crossing into Juarez, she added.
By comparison, 11,400 criminal aliens were processed through San Antonio, Texas, via the nearby Laredo international bridges, and 11,000 criminal aliens were deported through San Diego, California.
The location of the deportation proceedings "depends on bed space and operational availability," Zamarripa said.
Reyes Ferriz wants deportees to be repatriated to the interior of Mexico instead of his city.
The Department of Homeland Security is running such a program, involving deportees from Phoenix, Arizona. The deportation flights from Arizona to Mexico are happening because it is a high-traffic area for illegal immigrants, and because that's where the government of Mexico agreed to the program.
In a recent conversation, Homeland Security Secretary Janet Napolitano said the United States would work to give Juarez more details about who is being dropped off on its doorstep, Reyes Ferriz said.
The 2009 death toll in Juarez was 1,421 as of Monday, the mayor's office said, on pace to beat last year's 1,600 killings.
According to a report released last week by a Mexican watchdog group, Juarez, population 1.5 million, was the homicide capital of the world. It had an estimated rate of 130 killings per 100,000 people.
By comparison, the homicide rate in New Orleans, Louisiana, by far the deadliest city in the United States in 2008, was 64 homicides per 100,000 residents, based on preliminary FBI figures.
CNN's Mariano Castillo contributed to this report.