|Members of the Zetas gang arrested earlier this month include a 13-year-old girl [EPA]
One of the top leaders of Mexico's brutal Gulf cartel was found dead, shot on a highway near the US border, according to a statement released by the Mexican government.
The bodies of Samuel Flores Borrego, also known as "Metro 3," and a local police official were found in a pickup truck on the highway between the border city of Reynosa and Monterrey, the military and federal attorney general's office said in a joint statement on Friday.
"Initial evidence suggests that the facts resulted from an internal settling (of scores) within the criminal group," the statement said.
Flores, 39, is believed to be responsible for the January 2010 killing of a Zetas member that led to a rupture between the former allies, US anti-drug officials have said.
The Zetas started as a gang of hit men for the Gulf cartel, but after the split formed their own cartel, and fighting between the groups over territory and drug turf has caused violence to soar in parts of Mexico.
The US State Department had offered a $5 million reward for information leading to his capture and said on its website that Flores was in charge of the Gulf cartel's operations in Reynosa, across the border from McAllen, Texas.
Mexican President Felipe Calderon acknowledged in his state of the nation speech on Friday that violence "worsened with the rupture between the Gulf Cartel and the Zetas."
Calderon is trying hard to maintain public support for his battle with drug gangs ahead of national elections next year.
The war between the Zetas and the Gulf Cartel is blamed for some of the country's worst crimes, including the April discovery of 193 bodies in mass graves in the town of San Fernando near the US border.
The government blamed the Zetas for last week's casino arson in Monterrey that killed 52 people, mostly women who met with friends to gamble.
Meanwhile, in a central Mexican state, police arrested 31 suspected drug cartel members, including 16 police officers who allegedly were paid to protect the Zetas gang.
More than 42,000 people have died in less than five years as violence escalated.
Security forces have captured or killed many senior traffickers. Calderon says the violence is a sign of weakness in the gangs as they fight among themselves to dominate smuggling routes to the United States.