|Mexico's ongoing drug war continues to claim lives and disrupt order in the country [AFP]
Sixteen police officers have been arrested on suspicion of protecting a criminal gang wanted for the massacre of at least 126 people in northeastern Mexico.
Marisela Morales, Mexico's attorney general, said the police were from San Fernando, Tamaulipas where authorities have unearthed mass graves holding the bodies of 126 people.
"The federal government reiterates its commitment to solve these lamentable and reprehensible homicides, and end the corruption of the police force which has made a pact with organised crime," Morales said in a statement on Thursday.
The police are alleged to have been protecting four people - three men and woman - who authorities believe were directly responsible for the killings.
The victims apparently were passengers on public buses running routes through San Fernando to Reynosa and Matamoros, two Mexican cities on the border with the United States.
The massacres have been blamed on Los Zetas drug cartel, a notorious gang headed by former military commandos who turned to drug trafficking, kidnappings, extortion and other crimes.
Authorities had previously arrested 17 people linked to Los Zetas. The government offered a reward in the amount of $3.8mn for information leading to the capture of the four chief suspects.
Al Jazeera's Franc Contreras, reporting from Mexico City, said that while members of the Zetas drug cartel are suspected in the killings "authorities have accused the police of covering up these crimes".
"There is no clear sign of motive just yet. However, one of the big problems with conducting this investigation is the issue of official police corruption at the local level that has been a major barrier to bringing these cases to justice here," he said.
Meanwhile, 70 of the bodies recovered so far were transported on Thursday to Mexico City to further the identification process, a justice official told the AFP news agency.
"They have been taken for embalming and analysis by the Forensic Medical Service," the spokesman told AFP.
The bodies had been transported from Matamoros, in the state of Tamaulipas, where the remaining 56 bodies were still kept.
Dozens of people in Matamoros, across the border from Brownsville, Texas, were waiting to see whether their missing relatives had been found in the mass graves.
Authorities believe most of the victims were Mexicans, although at least one Guatemalan was confirmed among the dead.
San Fernando was the same municipality where Los Zetas last year kidnapped and slaughtered 73 immigrants from Central and South America on their way north to try to illegally cross into the United States.
Seven major drug gangs are operating in Mexico, and over 34,600 people have been killed since December 2006 in violence related to raging wars for control of smuggling routes and government efforts to stamp them out.
On Thursday, authorities found the bodies of eight men, heaped in a pile and with signs of torture and gunshots to the head, in the western state of Michoacan, officials there said.
Michoacan, among Mexico's most violent states, is the stronghold of La Familia, the drug cartel considered the country's largest producer and trafficker of illicit synthetic drugs bound for the United States.