Mexico's governmental human rights commission says it is investigating claims that Mexican immigration agents illegally detained a U.S. woman and two 17-year-old boys and tried to extort money from them.

The rights commission said Friday the three were detained Aug. 17 in the Gulf coast state of Tabasco while returning from a visit to relatives. The woman is the mother of one of the boys, but not the other.

Immigration agents frequently stop buses in the area to check for illegal Central American immigrants.

The country's Immigration Institute denied there was any abuse. It said the three weren't carrying passports and were taken in to determine whether they were in Mexico legally.

The rights commission identified the woman as Diana Leal of Texas. It did not identify the minors.