At least 13 people have been shot dead at a house party in the Mexican border city of Ciudad Juarez, officials say. A group of gunmen burst into the party late on Friday and began shooting, police said. At least another 10 people were injured. Police said the victims were aged 14-20. The attackers escaped with no arrests made, a state prosecutor said.Witnesses said attackers in several vans pulled up to the house near midnight and broke into the house, opening fire. The attack is similar to one earlier this month in which six people were killed at a party.It is not clear if the latest killings are related to Mexico's drug war, which has seen the police and army struggle to control the heavily armed cartels.