President Obama Honors Argentine Victims of 'Dirty War'

—BUENOS AIRES, Argentina -- President Obama paid tribute to the victims of Argentina’s so-called “Dirty War,” honoring thousands of Argentinians killed by visiting the Parque de la Memoria on the 40th anniversary of the 1976 military coup, acknowledging “controversy about the policies of the United States early in those dark days.”

"I believe we have a responsibility to confront the past with honesty and transparency,” Obama said. “A memorial like this speaks to the responsibilities that all of us have. We cannot forget the past, but when we find the courage to confront it, and we find the courage to change that past, that's when we build a better future."

Walking alongside Argentine President Mauricio Macri through the memorial, the leaders reached the inscription of Fernando Brodsky, where they were met by Fernando's brother Marcelo Brodsky. The trio continued through the memorial, pausing at the name of Toni Motta -- an American journalist who disappeared during the violence.

"This park is a tribute to their memory but it's also a tribute to the bravery and tenacity of the parents and spouses, siblings and the children who love and remember them," Obama said during remarks at the memorial. "Today, we also commemorate those who fought side-by-side with Argentinians for human rights."

The presidents were handed small bouquets of white roses and walked onto a pier, where they tossed the flowers into the river where many of the victims were drowned.

Obama said the United States government would declassify U.S. military and intelligence documents related to the "Dirty War," at the request of Macri and human rights groups.

Opened in 1997, the memorial is located alongside the Río de la Plata in the Belgrano neighborhood of Buenos Aires. The primary structure in the park is the Monument to the Victims of State Terrorism, a long wall -- similar to the Vietnam War Memorial in Washington, D.C. -- inscribed with 20,000 names and ages of victims. An additional 10,000 empty plaques represent victims who have not been identified. The wall is connected to a jetty that extends into the river, commemorating those who disappeared at sea.

ABC News' Ben Siegel contributed to this report.