Masked teachers detain a police officer during clashes in Chilpancingo, the capital of Guerrero state, Mexico. (AP)

Protesters furious at the presumed massacre of 43 students briefly blocked the main road to Mexico City's airport on Thursday, at the start of another day of demonstrations rattling the government.Riot police prevented hundreds of masked protesters from approaching the airport while patrol cars picked up passengers walking with their suitcases along the road.The city braced for a bigger rally later in the day, canceling the annual parade celebrating the 1910 revolution and erecting metal barriers to protect shops.It is the latest protest over the government's handling of a crime that has infuriated Mexicans fed up with corruption, impunity and a drug war that has left more than 100,000 people dead or missing since 2006.The case has turned into the biggest challenge of Enrique Pena Nieto's nearly two-year-old presidency, on top of another scandal over a mansion his wife bought from a government contractor.The crisis erupted after the mayor of the city of Iguala ordered police to confront students on September 26, sparking a night of violence that left six people dead and 43 missing, authorities say.Prosecutors say corrupt police delivered the 43 young men to members of the Guerreros Unidos drug gang, who confessed to killing and incinerating the students.Officials stopped short of declaring the students dead pending DNA tests. Federal police teams continue to search for them in the southern state of Guerrero, where the students vanished.Buses carrying parents of the 43 missing young men headed to the capital to join the march after a week-long tour of the country to voice their anger over the government's handling of the case.Highlighting their deep distrust of the government, they refuse to believe the students are dead and say they will only trust DNA test results from independent foreign forensic experts."We are moving forward, until the end, until the (students) reappear," Epifanio Alvarez, father of a missing student, told AFP. "The situation is bad. There are many missing people all over the country."Recent demonstrations have turned violent, with protesters burning the door of the capital's National Palace and torching government buildings in the state of Guerrero.With the annual parade called off, Pena Nieto led a ceremony with top officials at the Campo Marte military field, where he and the defense minister denounced violent protests."Mexico is hurting, but the only path to soothe this pain is through peace and justice," he said, hours after making all of his personal assets public to quell conflict of interest allegations over his wife's mansion.Defense Minister Salvador Cienfuegos said violence "only leads to national failure, social backwardness, ungovernability, instability."

Protests were called across the country as well as Europe and the United States on the anniversary marking the start of the 1910 Mexican revolution. Thousands marched in Bolivia and some 200 in El Salvador."The goal is to unite and mobilize the country, to lead it toward change," said Omar Garcia, who attends the same Ayotzinapa teacher-training college as the missing students.