Police patrol earlier this month in the increasingly violent state of Veracruz, Mexico.

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Seven people were killed in a highway attack this week

Three of the victims are identified as Americans

CNN  — 

Three of the seven victims of a highway attack this week in the Mexican state of Veracruz were American citizens, officials said.

A mother and her two daughters, dual Mexican-U.S. citizens who lived in Fort Worth, Texas, were aboard one of three buses that were attacked by gunmen in the city of Panuco, in the northern part of Veracruz.

“We express our deepest condolences to their family and friends during this difficult time,” State Department spokeswoman Neda Brown said.

A Mexican official in the state of Hidalgo, the hometown of the mother, identified the Americans as Maria Sanchez Hernandez and her two daughters, Karla, 19, and Cristina, 13.

The buses were on a road between the towns of Tempoal and Panuco near the border of Veracruz and Tamaulipas, Mexican and U.S. government officials said.

CNN.com: More violence in Veracruz

An American consulate general statement warned American citizens to “exercise caution and remain vigilant when traveling in the state of Veracruz. American citizens residing in, visiting or traveling through the northern portion of Veracruz that borders Tamaulipas and San Luis Potosi should maintain a heightened sense of alert.” Inter-city road travel at night should be avoided, the consulate general said.

CNN’s Mariano Castillo and CNNMexico.com contributed to this report.