BBC News with Jonathan Izard

Police in Mexico have confirmed that the murder victims from a mass killing near the US border were foreign migrants. Mexican marines discovered 72 unburied corpses at a ranch after a gun battle with suspected gang members. From Mexico City, here is Julian Miglierini.

According to the Mexican authorities, the bodies belong to citizens of Ecuador, El Salvador, Honduras and Brazil. The young man, who tipped off the authorities about the bodies at the ranch, is an Ecuadorian and managed to escape being killed. Authorities quoted the man as saying that the group was kidnapped by the Zetas, one of Mexico's most powerful criminal organizations, who demanded money from them. When they refused to pay, they were killed at the ranch. The Zetas, who have a strong presence in Tamaulipas, are known to use kidnapping and extortion of migrants as a means to finance their activities.