The search for 43 missing college students in the southern state of Guerrero has turned up at least 60 clandestine graves and 129 bodies over the last 10 months, Mexico's attorney general's office says.

None of the remains has been connected to the youths who disappeared after a clash with police in the city of Iguala on Sept. 26, and authorities do not believe any will be.

On Sunday, a few hundred people led by parents of the missing youths marched in Mexico City to call for justice in the case. Demonstrations have been held on the 26th of each month since the incident.

The number of bodies and graves found from October to May could possibly be higher than in its report, the attorney general's office said, because its response to a freedom of information request from The Associated Press covers only those instances in which its mass grave specialists got involved.

Federal authorities began turning up unmarked graves after beginning an investigation into the disappearance of the 43 young men following the confrontation between students and police that resulted in six confirmed deaths in Iguala, a municipality of 120,000 people 160 miles south of Mexico City.

The government of President Enrique Peña Nieto has said the students were detained by local police and handed over to a drug cartel, which killed and incinerated them at a garbage dump. Their remains were allegedly put in garbage bags and dumped in a nearby river.

He faces the deepest crisis of his administration over the government’s handling of the investigation, and anger over the case has resulted in sometimes violent demonstrations.

In January, Tomas Zeron, director of criminal investigations at Mexico’s federal attorney general's office, said that prosecutors had obtained an arrest warrant for the former mayor of Iguala José Luis Abarca and 44 others on charges of kidnapping the 43 students.

More than 20,000 people are listed as missing across Mexico, and there are many "disappeared" in Guerrero, a state that is a major opium producer and the battleground among several cartels warring over territory and drug smuggling routes. The government has said there is no evidence the 43 students were involved in the drug trade, but says they were mistaken for a rival gang.

Many people are questioning the government's version of happened to the students, including parents. Last week, Mexico's National Human Rights Commission (CNDH) issued a list of 32 omissions in the investigation — some of them very basic — and recommendations that it said are vital to solving the case, even though Mexico’s attorney general's office gave its official version of what happened in January.

Of the 129 remains found in the graves, 112 were men, 20 women and the rest are undetermined, according to the information released by the attorney general's office. Authorities listed only 16 of the remains as identified as of July 13.

Al Jazeera and The Associated Press