CIUDAD JUAREZ, Mexico  —  Police say six people were lined up and gunned down outside a business in this violent border city.

City police spokesman Alejandro Pariente says a written statement "for all rats" was found among the bodies and declared that the killings "will continue."

Pariente says investigators found more than 100 bullet shells at the scene. He says no arrests have been made and officials were investigating whether the Thursday-night attack was linked to drugs.

Drug violence has been spiraling across Mexico and especially in Ciudad Juarez, where more than 1,000 people have been killed this year. Ciudad Juarez is located across the border from El Paso, Texas.