Mexico City, Oct 3 (AFP) Veterans of Mexico's 1968 student movement and younger generations of activists marched in Mexico City to remember the day 50 years ago when army troops massacred hundreds of people at a peaceful protest.

Five decades on, it remains unclear exactly how many people were killed when the army opened fire on a rally of about 8,000 students in the Plaza of Three Cultures, in central Mexico City's Tlatelolco neighborhood.

The authoritarian government at the time put the death toll at 20, claiming "terrorists" attacked the troops, forcing them to defend themselves.

Independent reports say anywhere from 300 to 500 people were killed.

The massacre -- which came just 10 days before Mexico City hosted the 1968 Olympics -- remains one of the darkest episodes in a year of global turbulence.

The government's failure to bring those responsible to justice or explain what happened that day has become a rallying cry for the Mexican left and provokes annual protests that often turn violent.

There was a heavy police presence for Tuesday's march in central Mexico City, as thousands of people marched from the plaza where the massacre occurred to the capital's central square, the Zocalo.

They carried signs with messages such as "They keep killing us" and "The state kills and disappears students."

Those were references to both 1968 and the 2014 disappearance and suspected massacre of 43 students from the southern town of Ayotzinapa -- a murky crime involving corrupt authorities and drug cartel hitmen that still haunts the country.

But there was optimism that change was coming, with Mexico's first-ever leftist government set to take office on December 1 after a landslide election win for President-elect Andres Manuel Lopez Obrador.

"We think those responsible for 1968 might finally be punished... And if we can find out the truth about 1968, we might also find out what happened to our comrades from Ayotzinapa," said 22-year-old student activist Pedro Santiago. Lopez Obrador opened the commemorations by paying tribute to the victims of October 2, 1968, and promising to bring change.

"In this new era... we will honor the memory of the young victims of 1968. And the best way to do that is with humanism, without repression, struggling every day to make Mexico a just country," he said at a memorial in the plaza where the massacre occurred.

However, he declined to say whether he would reappoint a special prosecutor to investigate the killings or open the government's archives, as protesters demand.

In 1968, a series of explosive protests was sweeping the globe, from Europe to the United States and beyond. Mexico was no exception.

As the country prepared to host the Summer Olympics -- the first time they were held in Latin America -- President Gustavo Diaz Ordaz and the ruling Institutional Revolutionary Party (PRI) nervously eyed the student movement calling for democratic change after four decades of one-party rule.

On the morning of October 2, student leaders held talks with authorities on suspending their protests until after the Games in return for the release of political prisoners.

However, despite obtaining an agreement by the students to cancel a march later that day, the government was taking no chances.

As student leaders held a rally to deliver a progress report on their talks with the authorities, army snipers opened fire from the buildings surrounding the plaza.

"A helicopter flew overhead and fired a flare. At that moment, machine gun fire erupted all around... and bodies just started falling to the ground," said Victor Perez, a student leader who was 17 at the time.

Early the next day, he saw the aftermath from a friend's apartment overlooking the square.

"There was a mountain of bodies... workers, farmers, students, mothers, children, pregnant women," he said. No one has ever been sentenced for the killings.

The interior minister at the time, Luis Echeverria -- who went on to become president -- was charged with genocide over the massacre in 2006 and placed under house arrest. Three years later, the charges were dismissed. (AFP) KUN

(This is an unedited and auto-generated story from Syndicated News feed, LatestLY Staff may not have modified or edited the content body)