A sudden burst of gunfire echoes off the modest homes clinging to the steep hills of the 20 de Julio neighborhood, one of Medellin's most violent.
Minutes later, two hooded rebels drag the bloodied body of a young man by the legs down a labyrinth of steps and alleyways that crisscross the slum. At the bottom of the hill, they unceremoniously toss the body in a wheelbarrow and cart it off to be deposited at the door of the local hospital.
Across the valley, up on the opposite hills, paramilitary gunmen had just returned from a shootout with rebel infiltrators who had fired from a taxi they hired to take them into the enemy zone. Three paramilitary fighters were wounded.
In the newest front of Colombia's brutal 38-year-old civil war, leftist rebels and right-wing paramilitary forces are fighting for control of the lawless, impoverished neighborhoods of the nation's second-largest city.
Medellin has long been the country's most violent city, plagued with drug-related killings and gang warfare. But with the increased presence here in the past two years of the rebel and paramilitary groups, the violence has taken a new turn.
Colombia's two main guerrilla movements, the Revolutionary Armed Forces of Colombia, or FARC, and the smaller National Liberation Army, or ELN, have traditionally maintained small militias in Colombia's main cities. They served mostly as logistics units, supplying food and medicine to the rural fronts, organizing kidnappings and extortions and occasionally planning urban terrorism.
But two years ago, both insurgent groups and their bitter rivals, the paramilitaries, began bringing fighters to the city, resulting in street-by-street battles for control of the neighborhoods.
Throughout the poorer areas of the city, graffiti alerts outsiders to who controls which areas. The 20 de Julio neighborhood is covered with ELN and FARC slogans reading "We will conquer." The messages on the walls of paramilitary areas are more ominous: "Guerrilla fighter, put on your uniform or die as a civilian."
"The urban armed conflict is being seen more in Medellin than in other cities," said Gen. Leonardo Gallego, commander of the metropolitan police, which estimates 800 paramilitaries and 1,500 rebels are active in the city.
Local authorities have reacted to the encroaching war aggressively, and fatally.
A May 21 police and army operation in the 20 de Julio neighborhood quickly turned into the worst urban fighting in Colombia's war, when rebel militias met the troops with automatic weapon fire.
The 800 troops returned fire. By the time the battle ended 10 hours later, nine people, including two small girls, were dead, and 37 injured. Police said the dead were members of the militias, but then said the civilians were killed by rebel fire.
Edilma Tascon, 53, doesn't know who fired the bullet that killed her 11-year-old daughter, Yisel, that day but she blames the police.
"They are killing us in our homes," she said. "As long as the police don't come we live well, but when they come it's just one gunfight after another."
Last month's urban battle was awakeup call for the rest of the country.
"The violent events in Medellin reveal the risks of a general intensification of urban armed violence in the country, which obliges the state forces to rethink their strategy against the illegal armed groups," the Human Rights Ombudsman's Office said.
The strategy for Medellin authorities is to fight their way into the lawless barrios. "We cannot permit any areas to be off limits to the police," said Mayor Luis Perez, who was nearly the victim of his city's violence when rebels fired May 30 on a bus carrying him to a ribbon-cutting ceremony. He was unharmed.
By the mayor's admission, police haven't had real control over the hills in more than a decade. So when the rebels and paramilitaries opted to bring their fight to the city, they found fertile ground in crime-ridden, violence-numbed slums.
"Constant violence has become part of the city's being," said Gonzalo Medina Perez, a political analyst at the Universidad de Antioquia.
Observers trace the violence to the 1980s, when Pablo Escobar's powerful drug cartel outsourced murder to hordes of impoverished youths from squatter settlements surrounding the city. In 1991, at the height of Escobar's killing rampage, 6,300 people were murdered in this city of 2-million.
At the demise of the cartel in the early 1990s, the young men who had learned to live by the gun turned into criminal gangs and independent urban militias. Each controlled small areas of the barrios through murder, theft and extortion. The homicide rate held at a steady 3,000 per year until a few years ago, with the arrival of the war.
Rebels and paramilitaries have co-opted many of the independent gangs, killing off those who will not cooperate. The paramilitaries seek to expand their control while the rebels attempt to hold areas where they have been entrenched for years. The number of murders jumped last year to 3,445, mostly in the disputed neighborhoods. In the first four months of this year, 1,571 homicides were reported _ an average of 13 murders each day.
And while the death of nine people in the open battle here last month alarmed many Colombians, the war in Medellin is mostly fought one enemy at a time, like the recent killing of the intruder in the rebel neighborhood of 20 de Julio.
Authorities say they are fighting the rebels and paramilitaries, but the problem neighborhoods cited by the mayor and police chief are controlled by the FARC or ELN militias or a third leftist group, the Medellin faction known as the Armed Commandos of the People.
"The fact that paramilitaries are taking over large sectors of the city is not seen as a danger," said Ignacio Arango, a researcher with the Popular Training Institute, which documents Medellin's violence.
The paramilitaries claim to control more than 80 percent of the hillside neighborhoods, the same percentage the mayor cites as areas that "function in complete peace."
Perez denies implications that authorities allow the paramilitaries a free hand to combat the guerrillas as part of their security policy. "What we have recovered we have done with the visible forces of the state," he said.
But paramilitary commanders are bent on continuing their recovery efforts.
"We started off small to see how people would react to our presence, and two years ago the top commanders decided to start hitting harder," said a neighborhood paramilitary leader who goes by the name Piolin.
"We now control 80 percent of the barrios," Piolin boasted as two paramilitary fighters in camouflage took position with an AK-47 assault rifle and a mortar on the corrugated plastic rooftop of a modest home. "Our goal is to liberate the other 20 percent in the next two years."
Piolin acknowledges that paramilitary actions help the police drive out the rebel militias though he denies they work together. But when a police patrol arrives in San Pablo at dusk, two agents on a motorcycle chatted briefly with the neighborhood's recognized paramilitary leader and went on their way.
"Why would we want to fight the state?" Piolin asked. "Our sole purpose is to fight the guerrillas."
Aware of paramilitary intentions to occupy the city, rebel militias in the 20 de Julio neighborhood are on permanent watch for intruders and suspected paramilitary infiltrators.
"The paras are trying to establish themselves in the barrio," said an ELN squadron commander named Roberto, his face covered with a black kerchief. The butt of a snakeskin-patterned revolver protruded conspicuously from his pants and a small hand grenade hung from his belt.
Just then, Roberto's two-way radio crackled and a voice on the other end alerted him to presence of a suspicious person in the neighborhood. Roberto and two henchmen with assault rifles trotted off to confront the intruder. The gunfire came minutes later and the dead man was hauled off the hill.