Investigators in the state of Tamaulipas across the border from Texas searched for more mass graves on Saturday after authorities looking for abducted bus passengers uncovered 10 pits containing 72 bodies over the past week.
Investigators in Matamoros, which borders on Brownsville, Texas, worked to identify the bodies, telling relatives showing up in search of their loved ones that there would be no information until Monday.
Authorities would not release information about the conditions of the bodies or causes of death until the investigation is completed, Tamaulipas state Interior Secretary Morelos Canseco said Saturday.
While dozens of families and passengers complained of gunmen pulling people, mostly young men, off inter-city travel buses starting in late March, Canseco said not a single bus company filed a complaint with police officials in Tamaulipas in the last two weeks. Security experts say the abductions may have been attempts by cartels of forcibly recruit new members.
Families and state governments from around Mexico were calling Tamaulipas on Friday with reports of residents missing from buses that passed through the violent state, where the Gulf and Zetas drug cartels are warring for transport routes to the U.S.
"The state attorney general didn't receive any criminal complaint from any passenger bus line," Canseco said.
Canseco said state and federal officials would work with the companies to beef up security.
Attempts by The Associated Press to get comment from the bus companies Saturday were unsuccessful.
Meanwhile, U.S. officials warned Americans about the dangers of inter-city bus travel in Tamaulipas. The U.S. Consulate General in Matamoros said that between late March and early April it received three reports from U.S. citizens or their families of buses being boarded by criminals.
It also warned about potential hazards with highway travel in private vehicles in the region. A U.S. missionary was killed in the same area in January as her husband tried to evade an illegal road block set up by gunmen.
The consulate warning Friday was the third one about highway travel in Tamaulipas in the past five months.
Investigators uncovered the 72 bodies near San Fernando, a town about 90 miles south of Brownsville on a well-traveled stretch of highway patrolled by the Mexican military that runs near the Gulf Coast.
The same number of migrants were found massacred there last August.
Federal authorities said they are holding 14 people _ 12 men and two women _ as suspects in the state's second mass killing in less than a year.
The federal Attorney General's Office said there was evidence that most of the suspects belonged to the Zetas drug gang, the same group blamed for the August massacre. Some were detained with military-style uniforms, and others were found driving a pickup truck with false Mexican navy insignia.
(This version CORRECTS that Canseco has not named any bus companies that have stopped service to Tamaulipas)