SAN SALVADOR (Reuters) - Salvadoran authorities captured 120 members and associates of the Mara Salvatrucha (MS-13) gang, the prosecutor's office said on Thursday, part of a broad offensive to curb the escalation of gang-related killings in the Central American nation.

During the operation, which started Wednesday night, police arrested five leaders of MS-13 and seized motels, restaurants, brothels and dozens of buses controlled by the gang.

"Of the eight main ringleaders, we have captured five ... including the financier of MS," El Salvador's Attorney General Douglas Melendez told reporters.

Melendez also said that authorities confiscated an unspecified amount of money and drugs.

Lawyers for the detainees could not immediately be contacted for comment.

Violence in El Salvador, which saw a record level of homicides in 2015, has slowed in recent months.

While some attribute the decrease in murders to a truce between rival gangs, the government of President Salvador Sanchez Ceren, a former leftist guerrilla, says it is the product of an offensive against the "maras".

(Reporting by Nelson Renteria; Writing by Natalie Schachar; Editing by James Dalgleish)