In a move that could affect Champ Car's two Mexico races, the State Department on Wednesday issued a travel warning for Americans visiting Mexico, saying violent criminal activity, including murder and kidnapping, has increased in its northern border region. "U.S. citizens should be aware of the risk posed by the deteriorating security situation," the department said in a public announcement. It added that the great majority of victims are Mexican citizens. The announcement attributed the increased crime to a war between criminal organizations struggling for control of the lucrative narcotics trade. It said the leaders of several major criminal organizations have been arrested, creating a power vacuum. "This has resulted in a wave of violence aimed primarily at members of those trafficking organizations and criminal justice officials," the announcement said.