MEXICO CITY (AP) _ Mexican investigators found a clandestine grave with six bodies in Tamaulipas state, bringing to 122 the number of bodies found in pits in a region near the U.S. border that is wracked by battling drug cartels, authorities said Wednesday.

Tamaulipas state Interior Secretary Morelos Canseco said investigators are searching for more bodies at the pit found late Tuesday. The bodies were taken to a morgue in Matamoros, across the border from Brownsville, Texas.

The first graves were found earlier this month in the township of San Fernando, the same area of Tamaulipas where investigators found the bodies of 72 migrants massacred by suspects tied to the brutal Zetas drug gang last August. Most of the 72 migrants were Central Americans, who frequently travel through the area to reach the United States.

Authorities also blame the latest killings on the Zetas.

The Mexican government said it's offering a 15 million pesos

($1.27 million) reward each for information leading to the arrest of Salvador Martinez Escobedo, the alleged leader of the Zetas in San Fernando, and Omar Estrada Luna, a cell leader. The government is also offering 10 million pesos ($846,000) for Roman Palomo Rincones and 5 million pesos ($423,000) for Sarai Diaz Arroyo, who both allegedly participated in the latest massacre, Attorney General Marisela Morales said.

Morales said 16 San Fernando police officers have been detained for allegedly protecting members of the Zetas and covering up the kidnappings of bus passengers and others who traveled on a highway connecting San Fernando to the U.S. border.

Another 17 suspects tied to the brutal Zetas gang were earlier detained in relation to the killings, some of whom have purportedly confessed to abducting passengers from buses and killing them.

The motive for the bus abductions remains unclear, though prosecutors have suggested the gang may have been forcefully recruiting people to work for it.

San Fernando is a town about 90 miles (145 kilometers) south of Brownsville, Texas, on a well-traveled stretch of highway. The Zetas and rival Gulf Cartel are fighting in Tamaulipas over lucrative drug transit routes to the U.S.

Hours earlier, investigators in the Pacific coast state of Sinaloa found at least a dozen skeletal remains in a series of pits, while officials in neighboring Sonora pulled four bodies from two pits, authorities said Wednesday.

The graves in Sinaloa were discovered by a farmer who reported unusual odors coming from a field in the township of Ahome, near the state line with Sonora, state prosecutors' spokesman Martin Gastelum said.

He said that seven pits were found late Tuesday and excavations continued Wednesday. Two sets of remains appeared to belong to women who had been reported missing in October.

The state is the home base of Mexico's most powerful drug gang, the Sinaloa cartel.

The Sonora pits were discovered Wednesday in Nogales, a city across the U.S. border from Nogales, Arizona, Sonora state police said in a statement. One pit contained the body of a man and the second held the corpses of three men.

All the victims appeared to be about 30 to 35 years old, and the bodies appeared to have been buried between 10 and 15 days ago, the statement said. Mexican drug cartels have been blamed for a number of such mass graves, in which gangs deposit the bodies of kidnap victims or executed rivals.

Morales also said her office is offering a 10 million peso reward for information leading to the arrest of Julio Radilla Hernandez and Jose Luquin Delgado, both alleged members of the Southern Pacific drug cartel, which authorities say formed from the remnants of the Beltran Leyva cartel.

Morales said both men took part in the March 28 killing of Juan Francisco Sicilia, the son of Mexican poet Javier Sicilia, and six other people in Cuernavaca outside Mexico City.

Meanwhile, authorities in the border state of Ciudad Juarez said they have found four bodies buried in the desert that could belong to four men who were last seen when being detained by city police officers.

Prosecutors in Chihuahua state, where Ciudad Juarez is located, said in a statement Wednesday that the bodies and the clothes they are wearing matched the description given by relatives of the missing men.

In the northern industrial hub of Monterrey, a spokesman for state police said Wednesday that five suspected drug cartel members and a female motorist were killed in a shootout between soldiers and the suspects late Tuesday.

The spokesman, who was not authorized to be quoted by name, said the five suspects _ including one woman _ were traveling in a sport utility vehicle on an expressway and ignored an order to stop. In their bid to escape, they opened fire on soldiers and apparently tossed a hand grenade that hit a van, which exploded but whose driver was able to escape without major injuries.

However, a woman traveling in another SUV was hit by crossfire in the running gunbattle and died. Her 8-year-old daughter suffered a gunshot wound to the leg and is in stable condition.