A coalition of Mexican mayors has asked the United States to stop deporting illegal immigrants who have been convicted of serious crimes in the U.S. to Mexican border cities, saying the deportations are contributing to Mexican border violence.

The request was made at a recent San Diego conference in which the mayors of four Mexican border cities and one U.S. mayor, San Diego Mayor Jerry Sanders, gathered to discuss cross-border issues.

Ciudad Juarez Mayor Jose Reyes blamed U.S. deportation policy for contributing to his city’s violence, saying that of the 80,000 people deported to Juarez in the past three years, 28,000 had U.S. criminal records — including 7,000 convicted rapists and 2,000 convicted murderers.