The bodies of the victims lay scattered around the house.
Unnamed police officials told AP news agency that witnesses had counted at least 15 attackers.
"The men drove up in four SUVs, they were well-armed. They went into the house and shot at everyone, you could hear the gunfire all around," said a neighbour at the scene, quoted by Reuters news agency.
Ciudad Juarez, straddling a highly lucrative drug-smuggling route into the US, is the scene of a vicious ongoing turf war between rival cartels.
At least 15 other people died in the city, on the US border, at the weekend.
Most of the dead were teenagers or young adults
Some 45,000 troops and extra police have been deployed to crack down on the gangs in Mexico, including some 10,000 in Ciudad Juarez, which lies across the border from El Paso, Texas.
But the campaign has done little to curb the bloodletting - more than 7,000 people reportedly died in Mexican drug-related violence last year.
Beheadings, attacks on police, and shootings in clubs and restaurants are a daily occurrence in some regions.
In two of the worst attacks in 2009, gunmen stormed drug rehabilitation clinics in September, killing nearly 30 people.
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