by Sarah See
Two U.S. citizens and two others were killed by gunmen in Ciudad Juarez, Mexican authorities said Tuesday to CNN.
Rosa Williams, 35, and her son Pablo Noe, 19, were killed Friday evening by assailants armed with an AK-47 rifle and a 9 mm pistol when they were in a blue 2004 Dodge Durango SUV, Arturo Sandoval, a spokesman for Chihuahua's prosecutor's office, said.
Officials were working to return their bodies to the U.S., a spokeswoman for the U.S. Consulate in Juarez said to the Associated Press.
Alberto Nieto Nieto, 24, and Alma Yesenia Flores, 21, were identified Monday as the two other victims, a married couple from Mexico, authorities said.
The attack happened on a busy road across the U.S.-Mexico border from El Paso, Texas, according to witnesses.
A motive for the shooting has not been determined, investigators said.
More than 40 assault rifle and handgun shells were recovered at the scene, authorities said.
A warning was issued for American citizens in the city and other parts of the state of Chihuahua this year, cautioning that recent successes against drug cartel figures could put Americans in Mexico at risk, the U.S. Consulate General in Ciudad Juarez said.