Tens of thousands of people held protests in Mexico, joining tearful families of 43 missing students demanding their return amid fears a police-backed gang executed them.
Crowds on Wednesday gathered from Mexico City to the violence-wracked state of Guerrero, where the students disappeared, and as far south as Chiapas.
Parents of the victims traveled from Guerrero to head a march of thousands of people in Mexico City, tearfully holding up pictures of their sons, and signs reading "we want them back alive."
People watched from the sidewalk in tears, holding their fists up and chanting "you are not alone!"
The young men disappeared on September 26 after municipal police officers working with a gang shot at buses seized by the aspiring teachers in the Guerrero city of Iguala and took several of them away in patrol cars.
A mass grave containing 28 unidentified bodies was discovered on the outskirts of Iguala last weekend, in the same location where two hitmen from the Guerreros Unidos gang confessed to executing 17 students.
But authorities said it will take at least two weeks to confirm the identities of the bodies.
"We are sad but we will fight until the end," said a 19-year-old from the missing students' teacher training school who declined to give his name for fear of reprisals.
"We demand that the president doesn't just talk and send more forces to Guerrero," he said, with his face covered with a scarf as he protested in Mexico City.
In Guerrero state, more than 20,000 marched and blocked the highway between the regional capital Chilpancingo and the resort of Acapulco.
"This march is to demand that the federal and state governments show our sons alive," said Manuel Martinez, the spokesman for the families of the missing students, who were as young as 17 or in their early 20s
Thousands more protested in the southern state of Chiapas, with masked members of the Zapatista rebel movement taking part, without weapons but signs reading "We share your rage."
The government of President Enrique Pena Nieto has faced US and UN calls to solve the disappearance and investigate why gang-linked police attacked the students on September 26.
Pena Nieto deployed hundreds of federal forces to take over security in Iguala on Monday and disarm the local police. Some 30 investigators from the attorney general's office are in Iguala now.
- Search for students continues -
In Iguala, meanwhile, hundreds of civilian militiamen scoured the city of 140,000 to find the students.
They used machetes to cut through vegetation near the site of the mass grave.
"We will find the young men, dead or alive," said a self-defense commander called Moises, whose citizen self-defense group emerged last year to combat gangs plaguing towns in the rural mountains of Guerrero.
But authorities issued an order via radio for them to turn around.
"The police only conducts searches near roads. We will cover the whole ground," said Bruno Placido, leader of the UPOEG community police movement.
The students are from a teacher training college near Chilpancingo known as a bastion of radical protests.
Survivors say they had gone to Iguala to collect funds for their studies and were attacked when they were on their way home after seizing buses, a common practice among radical teachers-in-training in Guerrero to move around the state.
While authorities are still investigating the motive, the spotlight has turned on Mayor Jose Luis Abarca and his wife, Maria de Los Angeles Pineda Villa, president of the local family services agency.
Governor Angel Aguirre said one theory being explored is that the wife was unhappy the students were in town but he warned that the allegation she sent in the police should be taken with caution.
Pineda Villa's two brothers were members of the Beltran Leyva drug cartel until their deaths in 2009.
Authorities want to question Abarca over his role in the disappearance, but he and his wife have apparently gone into hiding.