MEXICO CITY  During its nearly four-year crackdown on major drug trafficking organizations, the Mexican government has repeated the mantra that most of the nearly 30,000 people killed have some association with the illicit trade.

But in the span of a week, a devastating wave of attacks has killed dozens of civilians, rattled a public not easily shocked anymore and forced the government to concede that innocents are being swept up in the violence.

In the latest attacks, gunmen killed four people early Thursday and injured 14 when they fired on three buses carrying workers home from a late shift at a manufacturing plant near Ciudad Juárez. The authorities said the assault  on workers from one of the large so-called maquiladoras, or factories, on and near the border that have fueled an economic and population boom there  had no precedent.

“This attack on the employees was a high-impact event that seeks to destabilize governments,” said Adrián Sánchez, spokesman for the Ciudad Juárez police. “They are fighting over their own interests, and only the bad guys know what it is about.”