In the United States, Texas authorities have advised American citizens not to travel Mexico during the spring break holidays for security reasons. The Texas Department of Public Safety said that drug cartel violence represented a significant threat for anyone crossing into Mexico. It has come after four Americans were kidnapped shortly after crossing the border last week. Two of them were murdered, while two were released unharmed.<br />'' <br />''Three American women who went to Mexico to sell clothes at a market have been missing for more than two weeks.