Two former Argentine dictators were handed heavy prison sentences on Thursday for their involvement in the kidnapping of babies from leftist activists killed during the 1976-1983 dictatorship.

Jorge Videla, 86, was sentenced to 50 years in prison and Reynaldo Bignone, 84, was given a 15-year jail term, presiding judge Maria Roqueta said as she read the ruling before a packed courtroom in Buenos Aires.

Hundreds of people -- relatives of the victims, children reunited with their families and activists -- cheered the ruling, which they watched on a giant TV screen set up outside the courthouse. Many were in tears.

Several other defendants were handed sentences ranging from 15 to 40 years for their roles in a "systematic plan" to kidnap the babies of activists, in a trial that launched in February 2011.

The rights group Grandmothers of the Plaza de Mayo has fought in court since 1996, demanding restitution for the stolen children. It says some 500 children were kidnapped and then raised by families close to the regime as their own.

"We have presented evidence showing that the kidnappers plotted to steal the children born to women in captivity," the group's president Estela de Carlotto said before the verdict was read out.

Human rights activists say some 30,000 Argentines "disappeared" during the military regime's so-called "dirty war" against leftists.

In the 35 abductions detailed during the trial, most of the mothers were held at ESMA -- Argentina's notorious Naval Mechanics School, a torture center located in the heart of Buenos Aires.

The maternity ward was on the second floor, where there was a hallway leading to the torture rooms that the executioners cruelly dubbed "The Avenue of Happiness."

The inmates gave birth while shackled and hooded. Very few were ever allowed even to see the faces of their babies, according to survivor testimony.

In most cases, the baby was given to a soldier or the friend of a soldier, while the mother was later thrown from a military plane into the sea, naked and still alive.

Argentina's amnesty laws of the late 1980s were annulled after the election of former president Nestor Kirchner (2003-2007), who died in October 2010. That annulment allowed the Latin American nation's judiciary to reopen a number of cases.

To date, all the people prosecuted for the kidnappings have been found guilty.

Videla defended his actions last week, saying in court that the children's mothers were "active militants in the machinery of terrorism. They used their children as human shields."

The former general had already been sentenced to life in prison for crimes against humanity.

A former US State Department assistant secretary for human rights, Elliott Abrams, revealed in January that the United States was aware of a systematic practice of stealing children.

"We knew that certain children had been given away while their parents were in prison or deceased," Abrams said. "They took them and gave them away."

The verdict fell on the 35th birthday of one of the victims, Francisco Madariaga Quintela, who learned of his real identity and was reunited with his biological father just over two years ago.

Madariaga Quintela said before the decision that he was confident "justice will be done" as he pulled from his wallet a faded black and white photo of his mother, who was kidnapped at age 28, while pregnant. Her body was never found.

"My dad told me she was a doctor. And sometimes I think about how I am now older than her," he said, looking at the image.