Mexico's raging drug war claimed the lives of six more police officers, ambushed on patrol in the marijuana-rich state of Sinaloa, authorities said Friday.

The attack followed the slaying Thursday of a senior police commander, part of a long string of killings apparently aimed at eroding public confidence in the government's ability to challenge drug gangs.

The six officers were killed when two carloads of heavily armed men cut off their vehicle in the Sinaloa capital of Culiacan, an official with the state attorney general's office said by e-mail.

More than 4,400 people have been killed in drug violence in Mexico, among them hundreds of police officers, since President Felipe Calderon launched an all-out offensive against drug cartels after taking office in December 2006.

Calderon says the surge in killings and gun battles is a sign of his government's success in cracking down on drug-trafficking networks.

But several analysts suggest that the high-profile killings in particular make the government and its main law enforcement agencies appear vulnerable.

The assassinations, along with the gangs' growing propensity for decapitating their victims and issuing threats using posters and the Internet, "have a clear objective to intimidate, frighten, paralyze society and, with that, force the federal government to retreat," Interior Minister Juan Camilo Mourino said Friday.

Inspector Igor Labastida, a senior officer in the federal police, was the fifth top commander slain in 13 months. A man armed with an Uzi killed him and one of his bodyguards as they ate lunch Thursday at a small, busy restaurant in Mexico City. The gunman fled in a waiting car while a second man videotaped the bodies and calmly walked away, witnesses told the Mexican daily El Universal.

Two bodyguards were wounded in the attack.

Labastida had survived an earlier assassination attempt, and his name figured on a hit list purportedly drawn up and circulated by drug gangs. Another senior commander on the list, Edgar Millan Gomez, was killed in May.

The Mexican government on Friday applauded U.S. Senate approval of a $400-million aid package for Mexico's drug war that will provide the Calderon government with training, telecommunications, aircraft and other equipment.

Mexico earlier objected to portions of the bill, known as the Merida Initiative, that would have required it to change the way human rights violations are investigated. Congressional officials agreed to ease those conditions.

Mourino, the interior minister, praised the measure because it represented "a concrete expression of the principle of shared responsibility" in the drug war.

Mexico has long complained that it endures the ravages of the war while the U.S. has done little to stop the flow of guns southward into the hands of the cartels. Mourino said he believed that was changing and that U.S. authorities had begun to track and stop weapons more efficiently.

"Are we totally satisfied with what is being done? Not yet," he said at a Friday morning news conference. "But we are satisfied at having made the U.S. government aware of the level of the problem, what it represents for our country and the need to take steps on the U.S. side."

wilkinson@latimes.com