MEXICO CITY (AFP) - Mexicans call it the cockroach effect - drug traffickers hit by security forces in one state skittering for refuge in another.
Now, the sprawling megalopolis of Mexico City is tightening security to head off such flight.
Fears rose this week because of a deadly clash that left 22 people dead as security forces fought suspected traffickers from the La Familia Michoacana cartel in the town of Tlatlaya, 240 kilometers (150 miles) from the capital and bordering Michoacan and Guerrero states.
Those fears prompted the mayor of Mexico City, Miguel Angel Mancera, to ask the army, navy and federal police to step up intelligence operations on the outskirts of Mexico City, which has a population of nine million plus 11 million more in its surrounding suburbs.
On the fringes of the capital, police are now searching incoming and outgoing vehicles and frisking people to try to catch drug traffickers.
The city is described by some as a relative island of peace in a country where drug-related violence has claimed some 80,000 lives since 2006.
The fear is that cartel members under assault by security forces in the nearby states of Michoacan in the west, Guerrero in the south and a neighboring state called simply Mexico, which is different from the Federal District, are trying to flee into the capital.
Increased violence in Mexico state is blamed mainly on the fleeing of cartel members from Michoacan. There, security forces launched a major military operation in 2013 because of fighting between the Knights Templar cartel and self-defense groups that rose up against it.
"Cooperation with federal forces is very important, mainly because they are cracking down hard on criminal groups in Michoacan, Guerrero and Morelos, and there is a high probability that they will move to Mexico City or the outskirts," said Raul Benitez Manaut, a security expert at the National Autonomous University of Mexico.
- Safe but no oasis -
As part of the new security plan, beefed up exchanges of intelligence and a meeting every two weeks with federal forces have been added to 56 police checkpoints that already had been set up outside the city.
In the working class neighborhood of El Rosario, which borders on Mexico state, a dozen cops check cars, buses and passengers.
"A lot of criminals pass through here. The ones from here go there (Mexico state) and the ones from there come here," said resident Jesus Arcos, 56, as he watches the police operation in El Rosario, one of Mexico City's dodgiest districts.
Mexico City had been largely free of drug-related violence until it was engulfed in 2013 by the kidnapping and murder of 13 young people in a nightclub called Heaven.
Since then, people go on alert with every new episode of violence, even though the authorities insist that crime is down 25 percent since 2012.
"If we take into account that every day there are between 15 and 20 million people in the city, that we have a daily average of 2.2 homicides and crime is falling, I can say it is a safe city, but not an oasis," the chief of public security for the capital, Jesus Rodriguez Almeida, told AFP.
As it stands, Mexico City is ranked 20th in Mexico in homicides and 17th in kidnappings among the country's 32 states.