Wall Street Journal, 8/24/2012

Federal police agents fired at an armored sport-utility vehicle carrying two U.S. officials on a rural road south of Mexico City, according to Mexico's Public Security Ministry, which oversees the country's 35,000-strong Federal Police force.

"This seems to be the first 'friendly fire' incident between US and Mexican agents. It probably won't have a large impact on policies of cooperation, but it may raise some tensions in day-to-day cooperation and a few questions in Washington," said Andrew Selee, director of the Mexico Institute at the Woodrow Wilson International Center for Scholars in Washington, D.C.