Massacre at drug clinic in Ciudad Juarez caps a particularly bloody 24-hour period.
La Familia is the most powerful drugs trafficking gang in Michoacan, the state which lies next to Guerrero.
The group, which has fought the powerful Gulf cartel from northeastern Mexico in recent months as it tries to expand its reach, uses violence and pseudo-religion to inspire its members.
It has said that it wants to protect the local population from rival drug gangs.
At least 14,000 people have died in violence related to the illicit drug trade in Mexico since President Felipe Calderon ordered an army-led assault on cartels in late 2006.
The US government has released part of a $1.4bn anti-drug package to Mexico to provide training and equipment to Mexican security forces.
The administration of US President Barack Obama has said that it will try to crack down on the smuggling of weapons from the US into Mexico.