A group of armed attackers killed 11 people at a soccer field after a match in the Mexican city of Salamanca, the latest outburst of violence in Mexico's Guanajuato state, officials said late on Sunday, Reuters reported. 

Six people were still receiving medical attention for injuries, Guanajuato's state attorney general's office said in a statement on Sunday evening. The office promised a thorough investigation.

A motive for the attack was not immediately clear, Salamanca Mayor Cesar Prieto said in a video statement shared on Facebook, according to Reuters.