MEXICO CITY — A gangland death squad killed at least 13 people, all but two of them high school students, and wounded as many as 17 others in an attack Sunday in the border city of Ciudad Juárez.

 A squad of gunmen stormed a party shortly after midnight in a working class neighborhood on the city’s east side, a few minutes’ drive from the city’s police headquarters. The party was to celebrate a championship soccer game between two high schools and one student’s birthday.

 While some of the attackers barricaded access to the residential street with their cars, others went room to room inside a small concrete house firing into the crowd of some 60 partygoers, witnesses said. Some students escaped by jumping over garden walls or taking refuge in neighboring houses. Others were gunned down as they fled.

 “They went directly into the house and started shooting,” an unnamed neighbor told El Diario, a Juárez newspaper. “Some people ran, and they chased them down.”

 Police and soldiers didn’t arrive at the scene until well after the attack ended.

Photographs of the scene, published online by Juárez media, show several rooms of a humble concrete house riddled with bullets, with large pools of blood on the floors and on the sidewalk outside. Police recovered 200 bullets from the scene.

 Police didn’t immediately provide names and ages of the victims, but said most were between 15 and 20. Local media reported that Adrián Encino, 17, who recently had been honored by the state governor for academic achievement, was among those killed.

 “He died in my arms,” said the boy’s sobbing grandfather, who’d rushed to the site.

 A couple working a small stand selling snacks to the teens also were shot, the man killed and his wife severely wounded. Several of the wounded students were reported in very serious condition, and police warned the death toll could rise.

 Such massacres have become alarmingly frequent since President Felipe Calderón launched a crackdown on Mexico’s criminal gangs more than three years ago. The gangland violence has killed more than 16,000 people since then, about a quarter of them in and near Juárez.

 More than 2,600 people were slain last year in the city of 1.3 million people.

 Officials said one of the slain students recently testified about another gangland killing in Juárez.

 Sunday’s atrocity capped a violent month in Juárez in which at least 220 people were murdered, including 10 on Saturday. Across Mexico, gangland violence killed more than 800 people last month, according to a tally by Mexican media.

 Also on Sunday, as many as 20 suspected gangsters attacked a police station with assault rifles and grenades in the Pacific port of Lazaro Cardenas. A policeman and two civilians, who were at the station to pay a fine, were killed.

 And in Sinaloa, the Pacific Coast state considered the cradle of Mexico’s drug gangs, gunmen ambushed a car carrying a state police official, killing him, another man and three women.

 The bound bodies of seven men were dumped Saturday in Iguala, a small city southwest of Mexico City. Notes left with the corpses warned that the men’s fate awaits all “thieves, kidnappers and corrupt lawyers.”