The mother of three U.S. citizens missing for two weeks in northern Mexico says there is no word of their whereabouts.

Raquel Alvarado says witnesses saw armed men take her 26-year-old daughter Erica Alvarado Rivera and her sons, 22-year-old Alex and 21-year-old Jose Angel, on Oct. 13 in El Control, a small town near the Texas border west of Matamoros. The three from Progreso, Texas, were visiting their father in Mexico.

Alvarado said Monday that witnesses identified the armed men as members of the Hercules group, a police unit that provides security to Matamoros' mayor. A spokeswoman for the city of Matamoros did not immediately respond to a request for comment.

A spokesman for the U.S. embassy confirmed that U.S. officials are monitoring the case and providing consular assistance.