Ciudad Juarez, Mexico (CNN) -- Authorities in this violence-plagued border city Thursday were investigating a series of attacks the day before that left 14 people dead, including four people who were slain aboard an ambulance.
Among the attacks Wednesday, gunmen ambushed an ambulance that was transporting two dialysis patients to a hospital in Juarez, police said. The driver of the ambulance and another person traveling with the group also died in the attack.
Photos from the scene showed a dusty white ambulance with the passenger-side window shot out, blood smeared across the car door and bullet marks on the windshield.
The ambulance traveled to Juarez from the city of Nuevo Casas Grandes, about 170 miles away, police said.
Juarez, one of Mexico's most violent cities, shares a border with El Paso, Texas.
The border city has become a symbol of the brutal realities of the nation's drug war, which has claimed about 43,000 lives since President Felipe Calderon declared a crackdown on cartels in December 2006.
Crime rates in Juarez have declined since last year, with the daily homicide rate dropping from about eight in 2010 to six in 2011.
Chacon reported this story from Ciudad Juarez, Mexico. Valencia wrote the story in Atlanta.