SAN SALVADOR (Reuters) - At least nine members of the gang Barrio 18 were killed in El Salvador on Saturday in a confrontation with the army, which has taken on a larger role in fighting violence in the poor Central American nation.

Prosecutors said the killings occurred in Zacatecoluca, considered to be the country's third most violent city which lies about 60 kilometers southeast of San Salvador.

A police spokesman in the nation's capital of San Salvador said officials have begun an investigation to determine the details of the encounter.

Violence in El Salvador has increased over the past year after a 2012 truce between the Barrio 18 and rival gang Mara Salvatrucha (MS-13) started to unravel.

The country averages about 15.5 homicides per day as gangs battle for control of drug trafficking and extortion operations, making it one of the world's deadliest nations.

In response to criticism over his failure to stem the violence, President Salvador Sanchez Ceren said on Saturday that he plans to promote the creation of three battalions of 1,200 troops specialized in criminal gang activity.

(Writing by Alexandra Alper; Editing by Diane Craft)