Protesters angry at the apparent massacre of 43 Mexican students clashed with police and besieged Acapulco's airport for hours over a scandal shaking President Enrique Pena Nieto's administration.

Thousands of people marched to the Pacific resort town's international airport, with parents of the students leading the demonstration along with comrades from the missing young men's teacher-training college in the southern state of Guerrero.

The rally followed violent protests that erupted over the weekend after authorities said gang hitmen confessed to murdering the 43 students and incinerating their bodies in September after corrupt local police handed the men over.

In a case causing national revulsion, Attorney General Jesus Murillo Karam downplayed chances of ever identifying the charred remains, warning that only two bones were salvageable for DNA tests.

But Murillo Karam has agreed to meet Tuesday with parents of the missing students, said Epifanio Alvarez, father of one of them.

"We want to tell him we want officials from the United States to come to beef up the search," Alvarez told AFP in a weak voice.

"Pena out! Pena murderer! Stay in China," protesters chanted, referring to the president's controversial decision to travel to a summit in Beijing amid public fury over the crime.

The protesters blocked the airport's entrance for more than three hours, with some masked men armed with sticks, though several tourists snuck in through a private terminal.

Before reaching the airport, protesters threw stones and a firebomb at riot police who were blocking their way, injuring at least 20 officers, a security official said.

Tourists had to reach the airport by foot, pulling their suitcases behind them. Three flights were canceled.

"Every Mexican is in this struggle," said Beatriz Barros, a Mexican traveler. "I don't care if I arrive home later because what they (the protesters) are doing is fair."

- Austrian experts -

Authorities say gang-linked police shot at busloads of students in the Guerrero city of Iguala on September 26, in a night of violence that left six people dead.

The police then handed the 43 abducted students to the Guerreros Unidos drug gang, prosecutors say.

Authorities say Iguala's mayor ordered police to confront the students over fears they would interrupt a speech by his wife, who aspired to succeed him.The students had traveled to Iguala to raise funds but hijacked four buses to return home, a common practice among the young men from the college known for its radical left-wing politics.

Officials stopped short of declaring the students dead, stressing they were waiting for DNA results.

Murillo Karam said experts indicated there were only two bones, including a kneecap, that could possibly be matched to DNA samples.

The two pieces will be sent to a lab, which suggested "a possibility" of identifying them, he told the Televisa network.

The government has asked experts from Austria's University of Innsbruck to identify the remains.

Parents of the missing students, who deeply distrust the government, say they will only believe their sons are dead once they get independent DNA test results.

"We want the government to do everything possible as soon as possible to find the boys alive, because they are deceiving us," said Carlos Ivan, father of one of the missing students.

- Pena Nieto in China -

Pena Nieto was in China on Monday for an Asia-Pacific Economic Cooperation (APEC) summit despite criticism over his decision to travel in the midst of the crisis.

Amid the protests, a new controversy erupted over his wife's purchase of a mansion from a Mexican firm that was part of a Chinese-led consortium that won a $3.7-billion bullet train contract, which Pena Nieto abruptly canceled last week.

News website Aristegui Noticias reported that First Lady Angelica Rivera bought the Mexico City home, valued at $7 million, in January 2012.

Pena Nieto canceled the train contract after the opposition questioned the transparency of the bidding process, in which the China Railway Construction Corp. group was the only bidder.

Presidential spokesman Eduardo Sanchez said Rivera, a former soap opera star, bought the home with her own money and that the news report did not influence the decision to revoke the train contract.