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.
Ciudad Juarez has been wracked by such shootings as violence among drug gangs has escalated in recent years.
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.
The Sinaloa and Carillo Fuentes Organisation (also known as the Juarez cartel) gangs are also competing in Ciudad Juarez over lucrative drug smuggling routes into the US, making the city one of the bloodiest frontlines in Mexico's drugs war despite the presence of some 4,500 police and soldiers.
Almost 5,000 people have died in the city in the past two years.
Since President Felipe Calderon ordered the army into the fight against the drug gangs in 2006, nearly 28,000 people have died.
The policy has had some successes arresting drug lords, but that has not led to a decline in the number of killings, or the level of kidnappings, extortion and human trafficking that the gangs also engage in.