Factbox: Worst incidents in Mexico's drug war
(Reuters) - Hundreds of protesters staged a demonstration outside government buildings in Monterrey on Sunday after an arson attack on a casino last week which killed 52 people.
Below are some of the worst attacks since President Felipe Calderon took office in December 2006 and declared war on powerful drug cartels. More than 42,000 people have been killed in drug-related violence since then.
* Sept 15, 2008 - Suspected members of the Zetas drug gang tossed grenades into a crowd celebrating Mexico's independence day in the western city of Morelia, killing eight people and wounding more than 100.
* Jan 31, 2010 - Suspected cartel hitmen killed 13 high school students and two adults at a party in Ciudad Juarez across from El Paso, Texas.
* March 13 - Hitmen killed three people linked to the U.S. consulate in Ciudad Juarez in March, provoking "outrage" from President Barack Obama.
* June 28 - Suspected cartel hitmen shot and killed a popular gubernatorial candidate in the northern state of Tamaulipas in the worst cartel attack on a politician to date. Rodolfo Torre, 46, and four aides from the opposition Institutional Revolutionary Party, or PRI, were ambushed on their way to a campaign event for the July 4 state election.
* July 18 - Gunmen burst into a birthday party in the northern city of Torreon, using automatic weapons to kill 17 party-goers and wound 18 others. Mexican authorities later said those responsible were incarcerated cartel hitmen let out of jail by corrupt officials. The killers allegedly borrowed weapons and vehicles from prison guards and later returned to their cells.
* July 24 - Police unearthed 51 bodies in a grave outside Mexico's business capital Monterrey in northern Mexico over several days. Some corpses were burned beyond recognition.
* Aug 25 - Marines found the bodies of 58 men and 14 women at a ranch near the Gulf of Mexico in Tamaulipas state, some 90 miles from the Texas border, after a firefight with drug hitmen in which three gunmen and a marine died.
* April 2011. Officials unearthed the first of what turned out to be more than 450 bodies buried in mass graves in the northern states of Durango and Taumalipas.
* Aug 20. Five headless bodies were found in Acapulco, taking the number of people killed in the popular Pacific resort to at least 25 in that one week.
* Aug 25. Masked gunmen torch a casino in Monterrey, killing 52 people, most of them women. The attack takes less than three minutes.