Mexican police have found 21 more bodies during a search of mass graves in the city of Durango

Officials said that digging would continue at the sites, and have not ruled out finding further remains. The number of bodies unearthed in the state of Tamaulipas rose to 183 after six more remains were found. Durango and Tamaulipas have seen high levels of violence as drug gangs battle for control of smuggling routes. The existence of the mass graves in Durango came to light in early April 2011, when four bodies were found in a car repair workshop. To date, 79 sets of remains have been exhumed from this site, and a further 17 bodies found at another location in the city. Officials say it is believed that the corpses had been buried for at least a year. None of the bodies has been so far identified.