Rivals MS13 and Barrio 18, with up to 60,000 members, have agreed to keep the peace as part of a church-brokered deal

For more than a decade the San José del Pino neighbourhood in Santa Tecla was off limits to police. It was considered the headquarters for the criminal enterprises of one of El Salvador's ruthless street gangs, the Mara Salvatrucha, or MS13. Drugs and weapons were trafficked freely and impunity reigned.

Today, municipal police and gang members are building parks in the neighbourhood. "Now we can walk around without worries," says Sgt Juan José Mijango. "You can barely tell who's a marero [gang member] and who's not."

Santa Tecla, 15 minutes outside San Salvador, is one of 15 peace zones designated after a government-sanctioned and church-brokered gang truce between the MS13 and the rival Barrio 18 last year. The gangs, which have up to 60,000 members, had battled for years over control of cities through terror, threats and extortion, giving El Salvador one of the highest murder rates in the world. In March 2012 they agreed to end their aggression and, in certain peace zones, hand in their weapons.

The impact of the truce has been dramatic, with the number of murders dropping by nearly half. Between 2009 and 2011, about 4,000 people were murdered each year in the country of 1.9 million people and the violence showed no signs of abating. But after the truce, the number of murders plunged; last year 2,195 were killed, according to national police figures.

Other countries in Central America, which also suffer from gang wars, are watching the experiment closely but cautiously. Óscar Ortiz, the mayor of Santa Tecla, called the truce a very bold answer to an intractable situation.

Human rights ombudsman Oscar Humberto Luna applauded the drop in homicides, but warned: "Violence can't just be measured by the number of murders."

Indeed, other crimes are on the rise. Police figures show the number of disappearances has increased from 51 in the first two months of 2012 to 150 in January and February of this year. In Santa Tecla, the number of burglaries and carjackings is rising. Extortion, too, shows little sign of abating.

Ortiz said dismantling the extortion rackets would be the second phase of the establishment of the peace zones with the gangs. "They told us, 'First let's control the murders'," he admits. "Ending extortion will take a much bigger effort because for now it is their only means of income."

Programmes to create jobs and fund small businesses are under way but for many mareros who have tattooed their allegiance to the gang on their faces, heads and forearms, blending in will be tough. Nonetheless Ortiz and the government are counting on an old saying to be true: "An army without battles falls apart."