SAN DIEGO -- Fifteen people are dead following a weekend gun battle in the streets of Tijuana and officials say the drug cartel is to blame.

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Thirteen people were killed in the initial shootout, Tijuana officials said, and nine others were wounded. Two more people had succumbed to their injuries on Monday, NBC 7/39 reported.

All of the dead were believed to be drug traffickers, possibly rival members of the same cartel who were trying to settle scores, said Rommel Moreno, the attorney general of Baja California state. The names of the dead were not released.

At one point, the alleged traffickers fired at one another as their sport utility vehicles sped down a busy six-lane boulevard lined with restaurants, car repair shops, medical offices and strip malls, officials said. Bullet holes could be seen in the walls of a factory building and on the perimeter wall of a housing complex along the road, but no bystander deaths were reported. It was not clear how long the gun battles lasted.

Residents were asked to avoid leaving their homes Sunday following the violent gun battle. Police recovered 21 vehicles, many with bullet holes or U.S. license plates; a total of 54 guns; and more than 1,500 spent shell casings at various points in the city where the battles broke out, said Agustin Perez Aguilar, a spokesman for the state public safety department.

Eight suspects were being held on suspicion of weapons possession among other possible charges. They are being treated at a city hospital, which officials said is heavily guarded.

A former U.S. prosecutor says lethal violence in Tijuana will continue as drug lords battle for control of the lucrative drug trade. Attorney John Kirby, who prosecuted cases against leaders of the notorious Arellano Felix drug cartel, told NBC 7/39 that there is a fierce internal battle for control among current leadership of the drug gang.

Kirby said the violence in Tijuana is prompting some Mexican drug dealers to move north, to San Diego, to escape the violence -- which could mean more kidnappings and shootings here.

"You basically have Tijuana-style violence which is sort of migrating north," he said.

Analysts said that is setting off turf wars among weakened organizations. One cartel from the Sinaola area is also trying to get a bigger share of the border drug trade, adding violence, Kirby said.

In January, eight people died in a gun battle at a Tijuana safe-house apparently used by drug hit men to hold kidnapped rivals. In that confrontation, hit men holed up inside the house battled police and soldiers with automatic weapons for three hours.

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• April 27, 2008: 13 Killed In Massive Tijuana Gunbattles