Seven people were killed when a gunman opened fire in the early hours of Friday in a bar in northern Mexico, which has seen a resurgence in drug-related violence in recent weeks.
The man, armed with an AK-47 assault rifle, killed four men who were clients in the bar in Chihuahua state as well as three women who worked there, said a spokesman for the state attorney general's office.
"It has not been determined whether the attack is connected to drug trafficking, but by the type of weapon involved, it is to be assumed," said spokesman Carlos Gonzalez.
The attack occurred in the city of Chihuahua, the capital of the state that is also home to Ciudad Juarez, considered one of the most violent cities in the world until recently.
The attacker entered the bar with his face covered by a bandana, said the spokesman.
Chihuahua has seen heavy fighting between the local Juarez cartel and the Sinaloa cartel, led by Joaquin "Shorty" Guzman, who is seeking to control the city that is one of the main routes for trafficking drugs into the United States.
In spite of a change of government in December and a new strategy that avoids direct confrontation with the powerful cartels, violence in Mexico has picked up in recent weeks with fighting along the border, in the western state of Michoacan and the tourist destination of Cancun.
Nearly 3,200 people have been killed in drug-related violence during the first three months of President Enrique Pena Nieto's government, according to Mexican government data.
During the government of his predecessor Felipe Calderon (2006-2012), almost 70,000 people died as a result of the drug trade and 27,000 disappeared in one of the most violent periods in Mexico's history.