CIUDAD JUAREZ -- Gunmen burst into a party early Saturday and shot to death 12 young people and wounded at least 10 others in this Mexican border city's third massacre this year, police said.

"The victims were in the back yard of the house having a party when hooded men, in dark uniforms and with rifles, arrived in several vans, broke in and began shooting indiscriminately at those inside," a police official said in this troubled metropolis across the border from the US city of El Paso, Texas.

The young gunmen screamed insults as they opened fired on the crowd, according to witnesses, who told the police the hail of fire went on for five minutes.

"We have an initial toll of 12 dead and more than 10 wounded who have been taken to different hospitals," the municipal police official said, speaking on condition of anonymity.

At least four women were among the dead, and a seven-year-old girl was wounded, police said.

Local media reported that the death toll rose to 15 after three people died of their wounds in hospital, and that five other people were in serious condition. The media reports said five women between the ages of 16 and 24 were killed.

The massacre, which bore the chilling hallmarks of a drug cartel attack, began at 1:40 am Saturday.

Seven vans loaded with armed men pulled up outside a house where a party was under way in a residential district known as Horizontes del Sur.

They barged in and began shooting, while gunmen guarded the approaches to the house in vehicles posted at the two nearest street crossings, witnesses told police.

Local media showed images of bodies strewn among cars parked in the garage of a house.

Puddles of blood and bloodstained walls were visible at the house along with abandoned pocketbooks, shoes and overturned food, bottles and other remnants of the party.

The scale of the bloodshed was such that there weren't enough ambulances to take away the dead and wounded.

Neighbors stepped in and drove victims to the hospital.

Many were too terrified to talk to reporters about what happened.

"Leave, please go away, don't make me vulnerable, I cannot talk," said a woman from her doorway. "If I did, the killers would return. They warned us."

Identification of victims was still under way at midday Saturday.

Several were high school students between the ages of 13 and 17. A 30-year-old woman who owned the house also was among the dead.

It was the third massacre of its kind in the city this year, and the seventh in all of Mexico.

On January 31, 16 youths were killed when gunmen opened fire at a party in the city, and on June 11, 19 people were gunned down in a drug rehabilitation center.

Ciudad Juarez, with a population of 1.2 million people across the Rio Grande from El Paso, Texas, is at the epicenter of a ferocious drug war between two major drug cartels.

In just the past three years, an estimated 6,500 people have been murdered here as the Juarez and Sinaloa cartels battle it out for lucrative drug routes into the United States.

Drug violence has flared all along with northern border, punctuated by gruesome murders and massacres.

On February 1, gunmen shot up a bar in the neighboring state of Coahuila, killing 10 people. The assailants were reported to be prison inmates who were let out for the night to work as guns for hire.

On March 28, bandits killed 10 youths at a roadblock in the state of Durango.

An armed gang killed 18 people at a party in Torreon, Coahuila in an episode reminiscent of the latest attack on July 18. Inmates from the local prison were suspected in that attack as well.

On August 28, the bodies of 72 undocumented immigrants from Central and South America were found on a ranch in the border state of Tamaulipas. A survivor accused the "Zetas" cartel.

The violence has claimed the lives of more than 7,000 people this year, making it the deadliest year since President Felipe Calderon launched a war on the drug cartels in 2006.